feat: Sprint A Wahab review batch — categories, property hierarchy, priority grouping

Items 1-5, 9, 11 from denya-wahab-feedback-s2:
- Category.show_in_form (alert-only flag): Gas Leak hidden from issue picker
  but kept urgent for SLA/alert and reporting; emergency quick path on the
  new-issue form creates urgent tickets via include_hidden categories.
- Seed: Aluminum/Glass, Carpentry, Mould & Damp (Medium default) maintenance
  categories; Lost Property renamed Missing Item (+ sub).
- One alembic migration: add show_in_form (backfill True, Gas Leak False) +
  data rename Lost Property -> Missing Item.
- Property -> Building -> Apartment cascade with searchable apartment combobox
  on the new-issue form and ticket list filters; /api/tickets/units gains
  building filter + /units/grouped variant; /api/tickets gains additive
  building/unit_id filters. apartment_mapping.json committed (deterministic).
- Group-by-priority toggle on /tickets (four sections + unknown bucket,
  age-sortable, composes with filters, URL deep links), FM dashboard active
  tickets, and CS dashboard priority card click-through.
- Tests: 13 new (category visibility, seed idempotency/sync, unit grouping,
  ticket building/unit filters).

app/templates/dashboard/ceo.html

@@ -249,8 +249,9 @@
                     this.charts.byProperty = { east: propData.east, west: propData.west, max: Math.max(propData.east, propData.west, 1) };
 
                     // By category — use categories endpoint
+                    // include_hidden=true so alert-only categories (Gas Leak) stay labeled in reporting
                     try {
-                        const cats = await app().apiGet('/api/tickets/categories/flat');
+                        const cats = await app().apiGet('/api/tickets/categories/flat?include_hidden=true');
                         const catCounts = {};
                         all.forEach(t => {
                             if (t.category_id) {