feat(agents): добавлены скиллы для ревью, GitHub, диагностики и менторинга

- Зачем:
  - расширить набор переиспользуемых скиллов для повседневных задач: ревью PR, работа с GitHub, проверка dotfiles, диагностика сети, ревью кода менти.
- Что:
  - добавлен differential-review (Trail of Bits) — security-focused ревью PR.
  - добавлен github (Callstack) — workflow через gh CLI, stacked PRs.
  - создан dotfiles-check — bash-скрипт проверки целостности stow-симлинков.
  - создан proxy-debug — диагностика сети и прокси hproxy.local.
  - создан review-homework — ревью кода менти в обучающем формате.
- Проверка:
  - bash ~/.agents/skills/dotfiles-check/check.sh ~/dotfiles

agents/.agents/skills/github/references/stacked-pr-workflow.md

@@ -0,0 +1,83 @@
+---
+title: Merge PR Chain
+tags: pull-request, stacked-pr, merge, squash, cherry-pick, github
+---
+
+# Skill: Merge PR Chain
+
+Merge a chain of stacked GitHub PRs into main as individual squash commits. Use when user has multiple PRs where each targets the previous one's branch (e.g., PR #2 -> PR #1's branch -> main) and wants to squash merge them all to main while preserving separate commits per PR.
+
+## Workflow
+
+### 1. Identify the chain
+
+Fetch PR details to map the chain structure:
+```
+main
+  └── #1 (base: main, branch: feat-a)
+        └── #2 (base: feat-a, branch: feat-b)
+              └── #3 (base: feat-b, branch: feat-c)
+```
+
+### 2. Merge and rebase sequentially
+
+**First PR** (targets main):
+```bash
+# Squash merge via GitHub CLI
+gh pr merge <N> --squash --title "<PR title> (#N)"
+git pull origin main
+```
+
+**Subsequent PRs** — rebase onto main, update base, then merge:
+```bash
+# 1. Checkout the branch for the next PR
+git checkout <next-branch>
+
+# 2. Rebase onto main, excluding commits from the old base branch
+#    This replays only this PR's commits onto main
+git rebase --onto origin/main <old-base-branch> <next-branch>
+
+# 3. Force push the rebased branch
+git push --force-with-lease origin <next-branch>
+
+# 4. Update the PR's base branch to main via GitHub CLI
+gh pr edit <N> --base main
+
+# 5. Squash merge the PR
+gh pr merge <N> --squash --title "<PR title> (#N)"
+
+# 6. Update local main
+git fetch origin main
+git checkout main
+git pull origin main
+```
+
+Repeat step 2 for each subsequent PR in the chain.
+
+## Key details
+
+- **Always use PR title as commit title** — GitHub may default to branch name or first commit otherwise. Pass `--title` explicitly.
+- **Use `--force-with-lease`** — Safer than `--force`, fails if remote has unexpected changes.
+- **Update PR base before merging** — After rebasing, change the PR's base branch to `main` so it merges correctly and shows "merged into main" in GitHub UI.
+
+## Handling conflicts
+
+When `git rebase --onto` encounters conflicts:
+
+1. Git will pause and show which files have conflicts
+2. **Stop and ask the user** to resolve conflicts manually
+3. After user resolves: `git add <resolved-files> && git rebase --continue`
+4. If user wants to abort: `git rebase --abort`
+
+**Never auto-resolve conflicts** — always ask the user to review and resolve manually.
+
+## Why this works
+
+`git rebase --onto <new-base> <old-base> <branch>` takes commits that are in `<branch>` but not in `<old-base>` and replays them onto `<new-base>`. This effectively strips the already-merged commits and moves only the PR's unique changes onto main.
+
+## Benefits over cherry-pick
+
+- PRs show as "merged into main" in GitHub UI
+- Clean linear history on main
+- No duplicate commits or confusing merge states
+- Each PR's diff remains reviewable until merged