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/index.html

@@ -135,6 +135,7 @@
           <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="M18 8A6 6 0 0 0 6 8c0 7-3 9-3 9h18s-3-2-3-9"/><path d="M13.73 21a2 2 0 0 1-3.46 0"/></svg>
           <span class="approvals-badge" id="approvalsBadge">0</span>
         </button>
+        <button class="btn-icon-header btn-readmymind btn-readmymind--hidden" id="readMyMindBtn" onclick="app.openReadMyMind()" title="Read My Mind: predict your next prompt" aria-label="Predict my next prompt"><span class="readmymind-icon" aria-hidden="true">🧠</span></button>
         <button class="btn-icon-header btn-attachments-history btn-attachments-history--hidden" id="attachmentsHistoryBtn" onclick="app.toggleAttachmentHistory()" title="Attachments" aria-label="Open attachment history" aria-expanded="false">
           <svg width="16" height="16" viewBox="0 0 24 24" fill="none" stroke="currentColor" stroke-width="2" stroke-linecap="round" stroke-linejoin="round" aria-hidden="true"><path d="m21.44 11.05-9.19 9.19a6 6 0 0 1-8.49-8.49l9.19-9.19a4 4 0 0 1 5.66 5.66l-9.2 9.19a2 2 0 0 1-2.83-2.83l8.49-8.48"/></svg>
           <span class="attachment-history-badge" id="attachmentHistoryBadge" style="display:none;">0</span>
@@ -1549,6 +1550,13 @@
                   <span class="slider"></span>
                 </label>
               </div>
+              <div class="settings-item" title="Read My Mind: capture your submitted prompts into a per-case intent profile and predict your next prompt on demand (header 🧠 button on Claude sessions). Predictions cost tokens and are never auto-sent">
+                <span class="settings-item-label">Read My Mind</span>
+                <label class="switch switch-sm">
+                  <input type="checkbox" id="appSettingsReadMyMind">
+                  <span class="slider"></span>
+                </label>
+              </div>
               <div class="settings-item" title="Show ultracode / Workflow runs as a master-detail tab (tasks on the left, agents with tokens + tool calls on the right)">
                 <span class="settings-item-label">Ultracode Agents</span>
                 <label class="switch switch-sm">
@@ -2740,6 +2748,37 @@
   </div>
 
   <!-- Approvals Inbox drawer (populated by approvals-ui.js; opened from the header bell) -->
+  <!-- Read My Mind: predicted-next-prompt modal (readmymind-ui.js). Suggestion
+       text is set via value/textContent only: predictor output derives from
+       observable (injectable) content, and the explicit click here is the
+       security boundary (nothing is ever auto-sent). -->
+  <div class="modal" id="readMyMindModal">
+    <div class="modal-backdrop" onclick="app.closeReadMyMind()"></div>
+    <div class="modal-content readmymind-modal">
+      <div class="modal-header">
+        <h3><span aria-hidden="true">🧠</span> Read My Mind</h3>
+        <button class="modal-close" onclick="app.closeReadMyMind()" aria-label="Close">&times;</button>
+      </div>
+      <div class="modal-body">
+        <div class="readmymind-loading">Reading your mind…</div>
+        <div class="readmymind-result" style="display:none">
+          <div class="readmymind-suggestion-row">
+            <span class="readmymind-kind" id="readMyMindKind" data-i18n-skip>continue</span>
+            <input type="text" id="readMyMindPrompt" class="readmymind-prompt-input" data-i18n-skip aria-label="Predicted prompt, editable" onkeydown="if(event.key==='Enter')app.sendReadMyMind(true)">
+          </div>
+          <div class="readmymind-why" id="readMyMindWhy" data-i18n-skip></div>
+        </div>
+        <div class="readmymind-error" style="display:none">No suggestion this time. Rethink to try again.</div>
+      </div>
+      <div class="modal-footer">
+        <button class="btn btn-secondary" onclick="app.closeReadMyMind()">Dismiss</button>
+        <button class="btn btn-secondary" id="readMyMindRethink" onclick="app.rethinkReadMyMind()">Rethink</button>
+        <button class="btn btn-secondary" onclick="app.sendReadMyMind(false)" title="Put the text on the session's composer without submitting it">Insert</button>
+        <button class="btn btn-primary" onclick="app.sendReadMyMind(true)">Send</button>
+      </div>
+    </div>
+  </div>
+
   <div class="approvals-drawer" id="approvalsDrawer" role="complementary" aria-label="Approvals inbox">
     <div class="approvals-header">
       <div>
@@ -2768,6 +2807,7 @@
   <script defer src="cron-ui.js"></script>
   <script defer src="settings-ui.js"></script>
   <script defer src="panels-ui.js"></script>
+  <script defer src="readmymind-ui.js"></script>
   <script defer src="ultracode-panel.js"></script>
   <script defer src="approvals-ui.js"></script>
   <script defer src="admin-ui.js"></script>