Stability checkpoint — Security MechanismsTab widget + spec

Single MR landed since stable-v1.0.41 (UI !110 → 7e67418) :

♻️  Refactoring (Phase B-7-4 follow-up)
- Mechanisms tab catalogue (9 categories, 12 production security
  mechanisms) becomes 2 self-contained files :
  - security-mechanisms-data.ts (165 LOC) — typed static data
  - widgets/security-mechanisms-tab.component.ts (68 LOC) — pure
    presentational widget, zero inputs, just renders the catalogue

🧪 Tests
- widgets/security-mechanisms-tab.component.spec.ts — 4 tests :
  class export, mechanisms field reference, expected categories
  present, every entry has non-empty fields + valid status
- 312 tests passing across 46 spec files (was 308/45 in 1.0.41)

Wins :
- security.component.ts : 566 → 426 LOC (-140, -25%)
- security.component.html : 626 → 586 LOC (-40)

7 remaining tabs (SQL/XSS/CORS/IDOR/JWT/Headers/Audit) untouched —
each requires more parent-state coupling, can be split incrementally
in future sessions.

Post-merge main pipeline #413 green on SHA 7cd059f.