feat(ui): opt-in entrance animations for tabs, terminal pane, agent windows and connection lines

All OFF by default (the `legacy` theme), so an untouched install behaves exactly
as before and every mark/apply hook short-circuits on its first line. Opt in via
App Settings > Appearance > Entrance Animations; per-surface control and a live
preview lab at ?animlab=1.

Surfaces and styles:
- Tabs: slide, pop, crt, unroll, boot, flip. A batch launched together cascades
  by a configurable stagger.
- Terminal pane: crt, boot, wipe, slide, fade.
- Agent windows: fly (the pre-existing tab-to-window flight, still the default),
  crt, materialize, unfold, beam, pop.
- Connection lines: draw, packet, fade.

Three constraints drove the design:

1. Tabs and connection lines are DESTROYED mid-animation on every re-render:
   _fullRenderSessionTabs() replaces the strip's innerHTML and
   _updateConnectionLinesImmediate() does `svg.innerHTML = ''`, both of which run
   constantly while sessions and agents spawn. Each is tracked by id and
   re-applied to the fresh element with a NEGATIVE animation-delay so it resumes
   at the same offset instead of restarting or snapping. Verified on the real
   path: a forced rebuild mid-draw resumed at -0.243s.

2. Terminal-pane styles animate transform/opacity/clip-path ONLY. xterm's
   FitAddon derives rows+cols from getComputedStyle(parent).width/height, the
   untransformed layout box, so transforms are invisible to it; animating
   width/height/padding would have resized the PTY. Verified by forcing
   fitAddon.fit() eight times mid-animation: dimensions held at 178x38.

3. A window entrance that transforms also moves the rect its connection line
   aims at (crt drifts it 109px, pop 81px). `beam` animates opacity/filter only
   (0px drift) so its line can draw toward a stable target; the others refresh
   the lines on animationend.

Also fixes: an agent window spawning hidden (its agent belongs to a background
tab) is display:none, so its animation never runs and animationend never fires,
which left the entrance class and its inline custom property stuck on the window
permanently. Hidden windows now skip the entrance entirely.

Styles persist to their own codeman:*Anim localStorage keys, keeping them
per-device without touching the .strict() SettingsUpdateSchema.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

CLAUDE.md

@@ -229,7 +229,9 @@ Codeman is a Claude Code session manager with web interface and autonomous Ralph
 
 ### Frontend
 
-Frontend JS modules have `@fileoverview` with `@dependency`/`@loadorder` tags. Load order: `constants.js`(1) → `i18n.js`(1.5) → `mobile-handlers.js`(2) → `voice-input.js`(3) → `notification-manager.js`(4) → `keyboard-accessory.js`(5) → `input-cjk.js`(5.5) → `sanitize-html.js`(5.6) → `app.js`(6) → `terminal-ui.js`(7) → `respawn-ui.js`(8) → `ralph-panel.js`(9) → `orchestrator-panel.js`(9.5) → `cron-ui.js`(9.7) → `settings-ui.js`(10) → `panels-ui.js`(11) → `ultracode-panel.js`(11.5) → `admin-ui.js`(11.7) → `session-ui.js`(12) → `webview-tabs.js`(12.5) → `ralph-wizard.js`(13) → `api-client.js`(14) → `subagent-windows.js`(15) → `ultracode-windows.js`(15.5) → `image-input.js`(16). `i18n.js` translates static + newly inserted application DOM while skipping terminal/response/file/user-name surfaces; `input-cjk.js` handles CJK IME composition via an always-visible textarea below the terminal (`window.cjkActive` blocks xterm's onData).
+Frontend JS modules have `@fileoverview` with `@dependency`/`@loadorder` tags. Load order: `constants.js`(1) → `i18n.js`(1.5) → `mobile-handlers.js`(2) → `voice-input.js`(3) → `notification-manager.js`(4) → `keyboard-accessory.js`(5) → `input-cjk.js`(5.5) → `sanitize-html.js`(5.6) → `app.js`(6) → `terminal-ui.js`(7) → `respawn-ui.js`(8) → `ralph-panel.js`(9) → `orchestrator-panel.js`(9.5) → `cron-ui.js`(9.7) → `settings-ui.js`(10) → `panels-ui.js`(11) → `ultracode-panel.js`(11.5) → `admin-ui.js`(11.7) → `session-ui.js`(12) → `webview-tabs.js`(12.5) → `entrance-animations.js`(12.6) → `ralph-wizard.js`(13) → `api-client.js`(14) → `subagent-windows.js`(15) → `ultracode-windows.js`(15.5) → `image-input.js`(16). `i18n.js` translates static + newly inserted application DOM while skipping terminal/response/file/user-name surfaces; `input-cjk.js` handles CJK IME composition via an always-visible textarea below the terminal (`window.cjkActive` blocks xterm's onData).
+
+**Entrance animations** (`entrance-animations.js`, all OFF by default): opt-in animations for the four things that appear when work starts, chosen per surface via `data-tab-anim` / `data-term-anim` / `data-win-anim` / `data-line-anim` on `<html>`. Defaults are the `legacy` theme, so an untouched install behaves exactly as before and every hook short-circuits on its first line. ⚠️ Tabs and connection lines are **destroyed mid-animation** on every re-render (`_fullRenderSessionTabs()` replaces the strip's innerHTML; `_updateConnectionLinesImmediate()` does `svg.innerHTML = ''`), so both are tracked by id and re-applied to the fresh element with a **negative `animation-delay`** to resume rather than restart. ⚠️ The terminal-pane styles may animate **transform / opacity / clip-path only**, xterm's FitAddon derives rows+cols from `getComputedStyle(parent).width/height`, so animating width/height/padding there would resize the PTY. ⚠️ Window styles other than `beam` transform the window, which moves the rect its connection line is aimed at; `beam` deliberately animates opacity/filter only so its line can draw toward a stable target. Persisted to its own `codeman:*Anim` localStorage keys (per-device, deliberately NOT in the `.strict()` `SettingsUpdateSchema`); picker in App Settings → Appearance, full per-surface lab at `?animlab=1`.
 
 **Command palette + shortcut registry**: `Ctrl/Cmd/Alt+K` opens the session palette; shortcuts live in a rebindable registry (`DEFAULT_SHORTCUTS`/`getShortcutRegistry()`/`matchesShortcutEvent()` in app.js, overrides in `settings.shortcutOverrides`). ⚠️ Palette-chord keys must ALSO be swallowed in `attachCustomKeyEventHandler` (terminal-ui.js) or xterm writes the control byte (0x0B) into the PTY. ⚠️ `saveAppSettings()` rebuilds settings from the DOM, so keys edited elsewhere (`shortcutOverrides`, `showTokenCount`, `showCost`) need explicit `_prev` carry-over. → [architecture-invariants#command-palette-and-shortcut-registry](docs/architecture-invariants.md#command-palette-and-shortcut-registry)