Account menu + Settings (change password); per-tree home person; full-width tree

- Sidebar bottom-left now shows the signed-in user; clicking opens a menu with
  Settings and Sign out. New /settings page: account info + change password
  (POST /auth/change-password, re-verifies current password). Export/restore/
  delete are stubbed there for the next pass.
- Per-tree default/home person: tree.home_person_id (migration) + TreeUpdate/
  Read; the tree and family views open focused on it; the person page gets a
  "Set as default" control and "Default person" badge. Cleared if that person
  is deleted. Complements the account-level "this is me" link.
- Tree visualization now fills the content area (AppShell drops the max-width
  column on the /tree route); other pages stay centered.
- Audit records are coerced JSON-safe (UUIDs/enums), so PATCHing UUID fields
  like home_person_id audits cleanly.

50 backend tests pass; migration up/down verified; frontend builds.

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

backend/app/services/audit.py

@@ -3,6 +3,7 @@ the change to a User (or the assistant principal acting for a User). Staged on
 the session; the caller commits as part of its unit of work.
 """
 
+import json
 import uuid
 
 from sqlalchemy.ext.asyncio import AsyncSession
@@ -11,6 +12,14 @@ from app.models.audit import AuditEntry
 from app.models.enums import AuditActorType
 
 
+def _json_safe(d: dict | None) -> dict | None:
+    """Coerce a change dict to JSON-native types (UUIDs, enums, dates -> str) so
+    it lands in the JSON audit column regardless of what the caller passed."""
+    if d is None:
+        return None
+    return json.loads(json.dumps(d, default=str))
+
+
 def record_audit(
     session: AsyncSession,
     *,
@@ -30,8 +39,8 @@ def record_audit(
         tree_id=tree_id,
         actor_user_id=actor_user_id,
         actor_type=actor_type,
-        before=before,
-        after=after,
+        before=_json_safe(before),
+        after=_json_safe(after),
     )
     session.add(entry)
     return entry