feat(db): table-health readout — per-table bloat metrics in admin card

You can't decide what to maintain without seeing what's bloating. Adds a
read-only health panel driven by Postgres' own statistics views.

- services/db_maintenance.py: get_table_health() queries pg_stat_user_tables +
  pg_total_relation_size + pg_database_size — per-table size, live/dead tuples,
  dead-tuple ratio (the bloat signal), and last (auto)vacuum/(auto)analyze.
- routes/admin.py: admin-only GET /api/admin/db-maintenance/health.
- SettingsView.vue: 'Table health' table in the maintenance card, all tables
  sorted by dead tuples, rows >=20% dead-ratio flagged; total DB size shown;
  refreshes after a Run-now so the dead-tuple drop is visible.
- Tests: health row/size shaping + null-timestamp passthrough; route + service
  surface.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

tests/test_routes_db_maintenance.py

@@ -3,7 +3,12 @@
 
 def test_admin_handlers_callable():
     from scribe.routes import admin as admin_routes
-    for name in ("get_db_maintenance", "update_db_maintenance", "run_db_maintenance_now"):
+    for name in (
+        "get_db_maintenance",
+        "update_db_maintenance",
+        "run_db_maintenance_now",
+        "get_db_maintenance_health",
+    ):
         assert callable(getattr(admin_routes, name))
 
 
@@ -13,6 +18,7 @@ def test_db_maintenance_routes_registered():
     rules = {r.rule for r in app.url_map.iter_rules()}
     assert "/api/admin/db-maintenance" in rules
     assert "/api/admin/db-maintenance/run" in rules
+    assert "/api/admin/db-maintenance/health" in rules
 
 
 def test_scheduler_surface():
@@ -28,8 +34,13 @@ def test_scheduler_surface():
 
 
 def test_service_surface_and_allowlist():
-    from scribe.services.db_maintenance import MAINTENANCE_TABLES, get_last_run, run_maintenance
-    assert callable(run_maintenance) and callable(get_last_run)
+    from scribe.services.db_maintenance import (
+        MAINTENANCE_TABLES,
+        get_last_run,
+        get_table_health,
+        run_maintenance,
+    )
+    assert callable(run_maintenance) and callable(get_last_run) and callable(get_table_health)
     # The allowlist is a closed tuple covering exactly the high-churn tables.
     assert isinstance(MAINTENANCE_TABLES, tuple)
     assert set(MAINTENANCE_TABLES) == {