feat(sessions): land auto-naming opt-in, in the prefix form, from the first user prompt only

Finishes #376. The contributed keystroke tracker sat on the raw byte stream
and named tabs wrong five ways (every prompt, every write path, a bare Esc
eating the next prompt's first character, pasted newlines as Enter, any CSI
clearing the draft) and replaced the whole name, which dropped the case from
the tab and reset the w<n> counter. This lands the feature with each of those
closed:

- First prompt means the first: applyAutoName() flips a placeholder to
  `auto` whether or not the string changed. nameSource is now the tri-state
  placeholder | auto | manual; the name setter is the only manual path.
- Only user-originated input counts: write()/writeViaMux() take
  SessionWriteOptions.fromUser, set by the browser WS path and POST /input
  only, so Ralph, respawn, cron, approvals and the trust-dialog keys can
  never name a tab. A startMode 'shell' CLI never feeds the tracker (a
  capability, not an id check); the send-key route feeds trackUserInput()
  because its line feed bypasses the session.
- Prefix form `w3-case: title`: parseSessionPrefix() already renders it as
  the title with the prefix in the tooltip and the next-session counter
  still matches it. Composed within MAX_SESSION_NAME_LENGTH.
- Tracker rules per key: bare Esc resolves at chunk end; mouse/focus
  reports, Tab, cursor keys, Shift+Tab are no-ops; Up/Down and Ctrl+P/N/R
  taint the draft so Enter submits nothing rather than a fragment;
  bracketed-paste newlines and Ctrl+J / Shift+Enter join with one space;
  the draft keeps its head past 8192 code points; an escape past 64 bytes
  is abandoned.
- Title: slash commands by shape (a path is a prompt), `!` escapes
  refused, first sentence only past 8 code points ("e.g." is not a title),
  72 code points on a word boundary.
- Synced `autoNameSessions` setting, default OFF (the prompt reaches
  mux-sessions.json, session:updated and /api/search), App Settings ->
  Appearance -> Tabs, read fresh per prompt after the eligibility check.

Tests: test/session-auto-name.test.ts (tracker, title, composition,
ownership, emit gating), the wiring test (once, prefix, setting off,
manual protected), test/routes/session-name-routes.test.ts (PUT /name
flips to manual and persists). Verified live on an isolated instance: API
and browser-typed prompts name the tab, a second prompt does not, shells
and renamed tabs are untouched, nameSource survives a restart.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

docs/wiki/Settings-Reference.md

@@ -76,6 +76,7 @@ every session or only the active tab.
 | Tall Tabs              | Taller tab strip.                                                                          |
 | Pop-out Button on Tabs | Adds the detach control to tabs, with a per-tab override.                                  |
 | Spawn Lineage Lines    | Arcs from a parent tab to sessions it spawned. Desktop only, on by default.                |
+| Auto-name Sessions     | Titles a new tab after its first prompt, keeping the case prefix (`w3-myapp: fix the login redirect`). Synced, off by default. See [The Dashboard](The-Dashboard#automatic-session-names). |
 | Overview Home Screen   | The phone home screen. On by default.                                                      |
 
 ### Models

docs/wiki/The-Dashboard.md

@@ -68,11 +68,15 @@ Tabs can also be dragged to reorder.
 
 ### Automatic session names
 
-New sessions start with a short project/sequence name so they can be created immediately.
-After the first task prompt is submitted, Codeman replaces that placeholder with a short
-title derived locally from the prompt's first sentence. Slash commands such as `/clear` do
-not become titles. A name you set with the inline rename action is treated as manual and is
-never overwritten by automatic naming.
+Off by default. Turn on **Auto-name Sessions** (App Settings → Appearance → Tabs; synced
+across devices) and a tab that still carries its generated name, such as `w3-myapp`, takes a
+title from the first real prompt you submit, keeping the prefix: `w3-myapp: fix the login
+redirect`. The strip shows the title and keeps the prefix in the tooltip, and the next
+session in that case still counts up to `w4-myapp`. It happens once per session, only for
+prompts you type or send through the input API (never a Ralph, respawn, cron or approval
+answer), and never for shells. Slash commands such as `/clear` do not become titles; the
+next prompt gets its turn. A name you set yourself, before or after, is never touched. The
+title is derived locally from the prompt's first sentence; no text leaves the machine.
 
 On phones the strip scrolls horizontally instead of wrapping, and the active tab is always
 scrolled into view. It is not reordered to the front, so the `Alt+N` numbering stays stable.