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/i18n.js

@@ -251,6 +251,20 @@
     Permission: '权限',
     Question: '问题',
     Idle: '空闲',
+    'Read My Mind': '读心术',
+    'Read My Mind: predict your next prompt': '读心术：预测您的下一条提示',
+    'Predict my next prompt': '预测我的下一条提示',
+    'Reading your mind…': '正在读取您的想法…',
+    'No suggestion this time. Rethink to try again.': '这次没有建议。点击「重想」再试一次。',
+    Rethink: '重想',
+    Insert: '插入',
+    "Put the text on the session's composer without submitting it": '将文本放入会话输入框但不提交',
+    'Predicted prompt, editable': '预测的提示，可编辑',
+    'Select a session first': '请先选择一个会话',
+    'Read My Mind works on Claude sessions only': '读心术仅适用于 Claude 会话',
+    'Prompt sent': '提示已发送',
+    'Inserted, press Enter in the terminal to send': '已插入，在终端中按 Enter 发送',
+    'Could not reach the session': '无法连接到会话',
     'Subagent Options': '子智能体选项',
     'Enable Tracking': '启用跟踪',
     'Active Tab Only': '仅活动标签页',