feat: rework EOL, repairs, and hosts for real workflow

Four domain-model changes driven by exercising the deployed 2.0 build:

- EOL moves from manufacturer to MPN via new PartModel catalog table,
  so alerts fire on the thing that actually ages.
- Repairs re-home to Host (required hostId + problem text) with an
  optional RepairJobPart join for affected parts; drop Part.replacementPartId.
- New /repairs/:id detail page with editable problem, part list, and
  a RepairComment thread (REPAIR_COMMENTED events fan out to each
  problem part's timeline).
- Host.assetId (required, unique) surfaces prominently on the repair
  page so techs can confirm they're touching the right box.

Single destructive migration reshapes existing dev data. All 7 packages
typecheck clean; 30 API tests pass (9 new covering host membership,
upsertByMpn idempotency + race, assetId 409, comment userId stamping).

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

apps/web/src/components/layout/Sidebar.tsx

@@ -4,6 +4,7 @@ import {
   ChevronsLeft,
   ChevronsRight,
   LayoutDashboard,
+  Layers,
   type LucideIcon,
   MapPinned,
   Package,
@@ -25,6 +26,7 @@ interface NavItem {
 const NAV_ITEMS: NavItem[] = [
   { to: '/', label: 'Dashboard', icon: LayoutDashboard },
   { to: '/parts', label: 'Parts', icon: Package },
+  { to: '/part-models', label: 'Part models', icon: Layers },
   { to: '/locations', label: 'Locations', icon: MapPinned },
   { to: '/manufacturers', label: 'Manufacturers', icon: Boxes },
   { to: '/repairs', label: 'Repairs', icon: Wrench },