feat(settings): put Session Options on the same surface as App Settings

Session Options was the last modal still wearing the old chrome: a strip of
top tabs over `.form-row` stacks, sitting next to a settings modal that had just
been rebuilt around a rail and grouped row cards. It now uses the same surface.

The `set-*` rules move from `#appSettingsModal` to
`:is(#appSettingsModal, #sessionOptionsModal)`. An `:is()` list takes the
specificity of its most specific argument, and both arguments are ids, so every
rule keeps exactly the weight it had - nothing downstream shifts in the cascade.

What the two modals do NOT share is what the rail means:

- App Settings stays a table of contents over one scrolling document.
- Session Options switches: one `.set-section` visible, `.hidden` on the rest.
  Summary owns its own scroller and Respawn is long, so stacking them into a
  single document would bury both. `switchOptionsTab` now queries
  `.set-rail-item` (it read `.modal-tab-btn` before) and resets the document
  scroll, so a switched-to section starts at its own top.

Phones get a horizontal, scrollable rail strip rather than App Settings' sticky
jump pill, which Session Options has no equivalent of. That is close to the tab
bar it replaces, so the phone gesture is unchanged.

Content is regrouped into the row language - label, description, control pinned
right - across all four sections: usage limits / respawn loop / cycle steps /
loop control, identity / token management / this session, tracker / limits, and
the summary timeline. The three cycle-step checkboxes became chips, which is why
`_syncSettingsChips` now covers both modals and Session Options registers one
delegated change listener per page for them.

Every id and handler the JS reads is preserved, and the component classes it
queries (`.duration-preset-btn`, `.duration-custom-input`, `.color-swatch`,
`.respawn-status-text`, `.run-summary-filters .filter-btn`) are untouched.
`data-claude-only` moved onto the rail entries, so external-CLI sessions still
lose Respawn and Ralph and land on Context.

`.modal-tabs`/`.modal-tab-btn`/`.modal-tab-content` now belong to
#createCaseModal alone. test/session-options-structure.test.ts pins the rail to
section pairing, the ids openSessionOptions reads, the one-visible-section
invariant and the Claude-only entries.

CLAUDE.md

@@ -264,7 +264,7 @@ Frontend JS modules have `@fileoverview` with `@dependency`/`@loadorder` tags. L
 
 **Per-device vs synced settings**: the `displayKeys` set in settings-ui.js is a **client-side merge policy**, not a wire filter. A display key seeds from the server only when localStorage has no value for it, which is what prevents one device overwriting another; `showPlanUsageLimits` is additionally `delete`d from the incoming payload outright. Separately, `SettingsUpdateSchema` is `.strict()` and simply **does not declare** `skin`, `showFileViewerButton`, `showCronButton`, `webglRendererEnabled`, `localEchoEnabled`, `cjkInputEnabled`, or `extendedKeyboardBar`, so sending one of those is a validation error. The rest (`showResponseViewer`, `showPlanUsageLimits`, `language`, and most `show*` keys) ARE in the schema and do persist server-side; they are per-device by client policy only. ⚠️ Adding a new per-device setting means deciding **both** questions: membership in `displayKeys`, and presence in the schema.
 
-**App Settings modal** (`#appSettingsModal`): a left rail that is a **table of contents over ONE scrolling document**, not a tab switcher. Every section stays mounted (`.set-section`, ids `settings-terminal|appearance|layout|models|clis|notifications|voice|shortcuts|system`), the rail follows the scroll, and `switchSettingsTab(id)` keeps its historical name but SCROLLS instead of hiding. Phones swap the rail for the sticky `#appSettingsJump` pill (compact layout at ≤860px in mobile.css). ⚠️ **The load/save contract is `getElementById` by id**: `openAppSettings()`/`saveAppSettings()` read every control by a fixed id, so moving a control between sections is free but renaming or dropping one silently stops it loading or saving. `test/app-settings-structure.test.ts` is the static guard. ⚠️ Model cards (`#appSettingsModelCards`) and the effort segment are **views over hidden `<select>`s** that remain the source of truth; the cards hold the BASE model and the "1M context window" switch composes `base + [1m]` back into `claudeModel`, which is what retires the old "takes precedence over the toggle below" trap. ⚠️ `.modal-tabs`/`.modal-tab-btn`/`.modal-tab-content` are still used by `#sessionOptionsModal` and `#createCaseModal`; the settings rail uses its own `set-*` classes and must not restyle them. ⚠️ `admin-ui.js` injects the multi-user Users entry into `.set-rail-items` + `.set-doc`, so those hooks must survive any restructure.
+**Settings surface** (`#appSettingsModal` + `#sessionOptionsModal`): the `set-*` language (left rail, groups of rows, control pinned right) is shared by BOTH modals through one `:is(#appSettingsModal, #sessionOptionsModal)` scope in styles.css — an `:is()` list takes its most specific argument's specificity, so both stay at the old id weight. **App Settings** is a left rail that is a **table of contents over ONE scrolling document**, not a tab switcher: every section stays mounted (`.set-section`, ids `settings-system|terminal|layout|appearance|models|clis|notifications|voice|shortcuts`, in that order — System first so the version and the updater are the first thing seen), the rail follows the scroll, and `switchSettingsTab(id)` keeps its historical name but SCROLLS instead of hiding. **Session Options** uses the same surface with a rail that really SWITCHES (`switchOptionsTab` shows one `.set-section` and puts `.hidden` on the rest, since Summary owns its own scroller and Respawn is long); phones give it a horizontal rail strip instead of the jump pill, which it does not have. `test/session-options-structure.test.ts` guards its rail↔section pairing and the `data-claude-only` entries external CLIs drop. Phones swap the rail for the sticky `#appSettingsJump` pill (compact layout at ≤860px in mobile.css). ⚠️ **The load/save contract is `getElementById` by id**: `openAppSettings()`/`saveAppSettings()` read every control by a fixed id, so moving a control between sections is free but renaming or dropping one silently stops it loading or saving. `test/app-settings-structure.test.ts` is the static guard. ⚠️ Model cards (`#appSettingsModelCards`) and the effort segment are **views over hidden `<select>`s** that remain the source of truth; the cards hold the BASE model and the "1M context window" switch composes `base + [1m]` back into `claudeModel`, which is what retires the old "takes precedence over the toggle below" trap. ⚠️ `.modal-tabs`/`.modal-tab-btn`/`.modal-tab-content` now belong to `#createCaseModal` alone; the settings surface uses its own `set-*` classes and must not restyle them. ⚠️ The **Header & Panels live preview** is a scale model rebuilt from the chips (`_syncLayoutPreview`); it owns NO icons, it CLONES `.set-chip-ico` out of the chip, so each icon has exactly one copy in index.html. A chip joins it via `data-preview` (slot) + `data-preview-order`, or `data-preview-text` for readouts that are not buttons. Its frame is painted from skin tokens only (hardcoded black alphas turned it into a grey slab on the light skins) and is `data-i18n-skip`. ⚠️ `admin-ui.js` injects the multi-user Users entry into `.set-rail-items` + `.set-doc`, so those hooks must survive any restructure.
 
 **Header button visibility**: most header controls are opt-in and hidden by a marker class (`btn-multimonitor--hidden`, `btn-response-viewer-header--hidden`, `btn-file-viewer--hidden`, `btn-cron--hidden`) that `applyHeaderVisibilitySettings()` (settings-ui.js) toggles after settings load; the multi-monitor button is instead stripped at render by `renderIndexHtml`. ⚠️ Hiding must go through the marker class: the base rules are `display:inline-flex !important`, so an inline style cannot override them. Current desktop default is WS/CPU/MEM + File Viewer + gear, with the token chip and lifecycle-log button OFF. ⚠️ New header controls must not leak onto phones; `test/mobile-header-buttons-policy.test.ts` is the static guard. → [architecture-invariants#header-button-visibility-multi-monitor-response-viewer-file-viewer-cron](docs/architecture-invariants.md#header-button-visibility-multi-monitor-response-viewer-file-viewer-cron)