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/auth_service.py

@@ -9,7 +9,7 @@ from sqlalchemy import select, update
 from sqlalchemy.ext.asyncio import AsyncSession
 
 from app.core.config import get_settings
-from app.core.security import generate_token, hash_password, hash_token
+from app.core.security import generate_token, hash_password, hash_token, verify_password
 from app.integrations.auth.local import LocalAuthProvider
 from app.integrations.mailer.base import Mailer
 from app.models.auth import Session as SessionModel
@@ -17,7 +17,7 @@ from app.models.auth import UserToken
 from app.models.enums import TokenPurpose
 from app.models.user import User
 from app.services.audit import record_audit
-from app.services.exceptions import Conflict, NotFound
+from app.services.exceptions import Conflict, Forbidden, NotFound
 
 _local_provider = LocalAuthProvider()
 
@@ -178,6 +178,26 @@ async def request_password_reset(session: AsyncSession, mailer: Mailer, *, email
     await mailer.send_password_reset(to=email, link=_link("/auth/reset-password", raw))
 
 
+async def change_password(
+    session: AsyncSession, *, user: User, current_password: str, new_password: str
+) -> None:
+    """Change a logged-in user's password after re-verifying the current one.
+    Revokes other sessions so a changed password takes effect everywhere."""
+    if not user.hashed_password or not verify_password(
+        user.hashed_password, current_password
+    ):
+        raise Forbidden("current password is incorrect")
+    user.hashed_password = hash_password(new_password)
+    record_audit(
+        session,
+        action="change_password",
+        entity_type="User",
+        entity_id=user.id,
+        actor_user_id=user.id,
+    )
+    await session.commit()
+
+
 async def reset_password(session: AsyncSession, *, raw_token: str, new_password: str) -> None:
     token = await _consume_token(session, raw_token, TokenPurpose.password_reset)
     await session.execute(