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_services_db_maintenance.py

@@ -76,6 +76,41 @@ async def test_one_table_failure_does_not_abort_the_rest():
     assert all(r["ok"] for r in summary["tables"][1:])
 
 
+def _health_session(db_bytes, rows):
+    s = AsyncMock()
+    s.__aenter__ = AsyncMock(return_value=s)
+    s.__aexit__ = AsyncMock(return_value=False)
+    size_res = MagicMock()
+    size_res.scalar.return_value = db_bytes
+    rows_res = MagicMock()
+    rows_res.mappings.return_value.all.return_value = rows
+    s.execute = AsyncMock(side_effect=[size_res, rows_res])
+    return s
+
+
+@pytest.mark.asyncio
+async def test_table_health_shapes_rows_and_db_size():
+    from datetime import datetime, timezone
+
+    from scribe.services.db_maintenance import get_table_health
+    vac = datetime(2026, 6, 14, 4, 0, tzinfo=timezone.utc)
+    rows = [
+        {"table_name": "notes", "live": 1000, "dead": 300, "dead_pct": 23.1,
+         "total_bytes": 5_000_000, "mod_since_analyze": 50,
+         "last_vacuum": vac, "last_analyze": None},
+    ]
+    with patch("scribe.services.db_maintenance.async_session",
+               return_value=_health_session(42_000_000, rows)):
+        health = await get_table_health()
+
+    assert health["db_bytes"] == 42_000_000
+    t = health["tables"][0]
+    assert t["table"] == "notes"
+    assert t["dead_pct"] == 23.1
+    assert t["last_vacuum"] == vac.isoformat()
+    assert t["last_analyze"] is None  # null timestamp passes through as None
+
+
 @pytest.mark.asyncio
 async def test_summary_is_persisted_as_admin_setting():
     engine, _ = _mock_engine()