feat(dashboard): technician performance report + real technician names

Wahab customer request (relay #748 v3 next-wave).

3a. Fix 'Tech #N' display:
- FM dashboard's "Technician Workload" card was built from
  `Tech #${t.assigned_to}`; it now reads Ticket.assigned_technician_name
  (falling back to 'Unassigned', matching /tickets).
- Template sweep confirms no other `Tech #` placeholder exists.

3b. Technician performance dashboard:
- New bearer-gated GET /api/tickets/tech-performance aggregating existing
  ticket columns only (no schema change): per-technician total assigned,
  completed, in progress, escalated, cancelled, pending, open tasks,
  completion rate, and created_at -> closed_at resolution time with explicit
  counts for finished tasks lacking a timestamp. Rows key on user id so
  same-name technicians stay separate; labels are real names. Fleet totals
  and an unassigned-ticket count are included.
- New /dashboard/tech-performance page (FM + CEO nav and links) with sortable
  table, completion bars and empty states; same-origin vendored assets only.
- Bucket map, service, schemas and tests in app/services/ticket.py,
  app/schemas/ticket.py, tests/test_tech_performance.py.

Tests: 111 passed (101 existing + 10 new).

app/templates/dashboard/ceo.html

@@ -1,9 +1,12 @@
 {% extends "base.html" %}
 {% block content %}
 <div x-data="ceoDashboard()" x-init="init()">
-    <div class="mb-6">
-        <h1 class="text-2xl font-bold text-gray-900">Executive Dashboard</h1>
-        <p class="text-gray-500 mt-1">Read-only strategic overview</p>
+    <div class="mb-6 flex flex-wrap items-start justify-between gap-3">
+        <div>
+            <h1 class="text-2xl font-bold text-gray-900">Executive Dashboard</h1>
+            <p class="text-gray-500 mt-1">Read-only strategic overview</p>
+        </div>
+        <a href="/dashboard/tech-performance" class="px-3 py-2 text-sm border border-gray-300 rounded-lg hover:bg-gray-50 text-gray-700">Technician Performance →</a>
     </div>
 
     <!-- Executive KPI Cards -->