Phase 3: coaching preferences + weekly check-in engine

Add coaching preferences (auto-derived from the profile, user-overridable) and
a periodic check-in engine that quotes the person's own words and asks whether
their direction still feels valid — mirror, not compass.

- Preferences are deterministic: a documented triad mapping (gut → direct/
  higher-friction, heart → warm/drift-sensitive, head → reflective/question-led)
  produces defaults for the six fields (coaching_frequency, coaching_style,
  misalignment_threshold, friction_tolerance, prefer_questions_over_directives,
  time_of_day_preference). PUT overrides; regenerate re-derives.
- CheckinCoach (app/services/coaching.py): Anthropic-backed; writes a check-in
  that quotes the person's goals back and asks if the direction still holds.
- Endpoints (app/routers/coaching.py): GET/PUT/regenerate preferences;
  GET/POST checkins; respond (records still_valid); admin POST /run is the
  weekly batch (due = cadence elapsed + locked profile), intended for a cron.
- Models + migration 005: coaching_preferences (per user) and coaching_checkin.
- Frontend: coaching.html (preferences form + check-in feed); linked from
  profile.html.

Tests: 68 passing (added deterministic-preference unit tests and coaching
endpoint/batch tests; run in-container). README updated for Phase 3.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

app/static/profile.html

@@ -142,6 +142,11 @@
              <a href="/static/reflect.html">Not quite right? Talk it through with your coach →</a>
            </p>`;
 
+      const coachingLink =
+        `<p class="back-link" style="text-align:center;margin-top:10px">
+           <a href="/static/coaching.html">Coaching preferences & check-ins →</a>
+         </p>`;
+
       content.innerHTML = `
         <div class="profile-narrative">${escapeHtml(
           profile.overlap_narrative
@@ -157,6 +162,7 @@
 
         ${goalsBlock}
         ${actions}
+        ${coachingLink}
       `;
 
       if (locked) return;