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/schemas/ticket.py

@@ -26,6 +26,7 @@ class CategoryOut(BaseModel):
     name: str
     parent_id: int | None = None
     sla_urgency: str | None = None
+    show_in_form: bool = True
 
     model_config = {"from_attributes": True}