feat: Read My Mind phase 2, the predictor and the brain button

The feature as pitched in docs/readmymind-plan.md: pressing the header
brain button predicts the prompt you were about to type, from the case's
intent profile plus everything the session already knows.

Backend:
- readmymind-context.ts: pure budgeted context assembler (9 ranked
  sources: pending approval dialog, user goals, last assistant turn tail,
  recent prompts, tool activity, git workspace signals, away context,
  sibling sessions, rethink state; 30 KB budget, whole-section drop from
  the bottom of the ranking, trust tiers stated in the prompt)
- readmymind-collectors.ts: transcript tail reader (the live watcher
  keeps only a 500-char snippet) and git signal collection (execFile,
  2s timeout, skipped for remote-SSH cases)
- readmymind-predictor.ts: one-shot claude -p in a throwaway tmux
  session, opus by default (readMyMindModel setting), strict JSON
  contract with 1-3 suggestions (continue / verify / redirect), newline
  stripping, 90s timeout; mutable singleton so route tests can stub it
- POST /api/sessions/:id/readmymind: claude-mode only (400), one
  prediction in flight per session (409 CONFLICT), rethink body
  { steer, rejected }; ownership via findSessionOrFail

Frontend:
- readmymind-ui.js (loadorder 11.3): header brain button, marker-hidden
  until readMyMindEnabled is ON, desktop only (phone key is phase 3);
  modal with editable suggestion + rationale and Send / Insert /
  Rethink / Dismiss; suggestion text rendered via value/textContent only
  and nothing ever auto-sends
- App Settings -> Panels checkbox for readMyMindEnabled; en + zh-CN
  strings

Verified end to end against a live isolated instance: transcript
capture, a real opus prediction grounded in the stated goals, rethink
steering, the 409, and the browser modal incl. Insert leaving the text
unsubmitted on the composer. 41 new unit/route tests; full test:ci
sweep green (4680 tests).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

src/web/public/settings-ui.js

@@ -344,6 +344,8 @@ Object.assign(CodemanApp.prototype, {
     document.getElementById('appSettingsShowUltracodeAgents').checked = settings.showUltracodeAgents ?? defaults.showUltracodeAgents ?? false;
     // Approvals Inbox: synced, default OFF (opt-in; only an explicit true enables).
     document.getElementById('appSettingsApprovalsInbox').checked = settings.approvalsInboxEnabled === true;
+    // Read My Mind: synced, default OFF (opt-in; capture + prediction cost real tokens).
+    document.getElementById('appSettingsReadMyMind').checked = settings.readMyMindEnabled === true;
     document.getElementById('appSettingsUltracodeFloatingWindows').checked =
       settings.ultracodeFloatingWindows ?? defaults.ultracodeFloatingWindows ?? false;
     document.getElementById('appSettingsShowMultiMonitorButton').checked = settings.showMultiMonitorButton ?? defaults.showMultiMonitorButton ?? false;
@@ -1544,6 +1546,7 @@ Object.assign(CodemanApp.prototype, {
       showSubagents: document.getElementById('appSettingsShowSubagents').checked,
       showUltracodeAgents: document.getElementById('appSettingsShowUltracodeAgents').checked,
       approvalsInboxEnabled: document.getElementById('appSettingsApprovalsInbox').checked,
+      readMyMindEnabled: document.getElementById('appSettingsReadMyMind').checked,
       ultracodeFloatingWindows: document.getElementById('appSettingsUltracodeFloatingWindows').checked,
       showMultiMonitorButton: document.getElementById('appSettingsShowMultiMonitorButton').checked,
       showPlanUsageLimits: document.getElementById('appSettingsShowPlanUsageLimits').checked,
@@ -2106,6 +2109,15 @@ Object.assign(CodemanApp.prototype, {
       ultracodeBtn.classList.toggle('btn-ultracode-agents--hidden', !showUltracodeAgents);
     }
 
+    // Read My Mind 🧠 — hidden unless the synced opt-in `readMyMindEnabled` is
+    // ON (only an explicit true enables, mirroring the Approvals bell). Marker
+    // class (base is display:inline-flex !important); phones hide it in
+    // mobile.css regardless (the phase-3 surface there is an accessory key).
+    const readMyMindBtn = document.querySelector('.btn-readmymind');
+    if (readMyMindBtn) {
+      readMyMindBtn.classList.toggle('btn-readmymind--hidden', settings.readMyMindEnabled !== true);
+    }
+
     // Plan-usage chip — shown by default on desktop, OFF on handhelds (App
     // Settings → Display → "Plan Usage Limits"). The template always ships it
     // hidden because display is per-device and the server cannot know a