docs(skills): ограничена область применения differential-review

- Зачем:
  - навык не должен предлагаться AI-ассистентом автоматически при каждом изменении кода, так как это дорогостоящая и глубокая операция.
- Что:
  - в описании (description) явно указано, что навык предназначен только для ручного вызова (Manual invocation only).
  - обновлено поле description текстом "ONLY when explicitly requested by the user".
- Проверка:
  - визуальная проверка agents/.agents/skills/differential-review/SKILL.md.

agents/.agents/skills/differential-review/SKILL.md

@@ -1,10 +1,10 @@
 ---
 name: differential-review
 description: >
-  Performs security-focused differential review of code changes (PRs, commits, diffs).
-  Adapts analysis depth to codebase size, uses git history for context, calculates
-  blast radius, checks test coverage, and generates comprehensive markdown reports.
-  Automatically detects and prevents security regressions.
+  Performs security-focused differential review of code changes (PRs, commits, diffs)
+  ONLY when explicitly requested by the user. Adapts analysis depth to codebase size,
+  uses git history for context, calculates blast radius, checks test coverage,
+  and generates comprehensive markdown reports. Manual invocation only.
 disable-model-invocation: true
 allowed-tools:
   - Read