fix(m6): post-review pass — cache prefix, snapshot lock, perm-before-parse, LIKE escape

Addresses spec-reviewer + code-reviewer feedback on the M6 bundle:

Critical:
- frontend/src/lib/missions.ts: add `listPrefix()` so TanStack invalidation
  catches every filtered list variant; the previous `list()` returned
  `['missions','list',{}]` and only matched the exact empty-filter cache,
  leaving filtered tables stale after create/transition/delete.
- backend/app/services/missions.py: acquire the same per-scenario
  `pg_advisory_xact_lock` key used by `set_scenario_tests` before
  snapshotting; without it a concurrent M5 reorder could freeze a torn
  snapshot under READ COMMITTED. Sorted by key to avoid deadlocks with
  another snapshotter.

Important:
- backend/app/api/missions.py: `@require_perm("mission.update",
  "mission.archive")` on the transition endpoint so users without either
  perm get 403 before the body is parsed (no shape leak via 400).
- backend/app/services/missions.py: escape `%` / `_` / `\` in user-typed
  `q` / `client` LIKE search; users can no longer trigger wildcard
  semantics by typing literal `%`. Added `escape='\\'` arg on every .like().
- backend/app/services/missions.py: filter `MissionTest.deleted_at` and
  `MissionScenario.deleted_at` in the list-item and detail counts so M7+
  soft-deletes don't drift the totals silently.

Nits:
- backend/app/api/users.py: order `/users/roster` by email for stable
  rendering + deterministic e2e selectors.
- frontend/src/pages/MissionDetailPage.tsx: distinct accent per
  transition target (cyan/orange/green/teal) matching the status legend.
- e2e/tests/m6-missions.spec.ts: switch fragile `getByRole(name=/In
  Progress/i)` to the stable `mission-transition-in_progress` data-testid.

New tests:
- test_create_mission_rejects_soft_deleted_scenario
- test_transition_perm_gate_runs_before_payload_parse
- test_search_treats_wildcards_as_literals

Suite: 106 pytest passing (was 103), 43 Playwright passing.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

backend/app/api/users.py

@@ -69,6 +69,7 @@ def list_roster():
     """
     q = request.args.get("q") or None
     rows = users_svc.list_users(q=q, is_active=True, limit=200, offset=0)[0]
+    # Sort by email for predictable rendering and stable e2e selectors.
     return jsonify(
         {
             "items": [
@@ -77,8 +78,10 @@ def list_roster():
                     "email": u.email,
                     "display_name": u.display_name,
                 }
-                for u in rows
-                if u.deleted_at is None
+                for u in sorted(
+                    (u for u in rows if u.deleted_at is None),
+                    key=lambda x: x.email,
+                )
             ]
         }
     )