fix(review): fix 5 worktree issues found in audit

1. Remove gh pr checkout --detach (modifies working tree, defeats
   worktree purpose). Use git fetch only.
2. Add dependency installation step (npm ci etc.) in worktree —
   without it, all TS/JS linting/building fails.
3. Cache and reports written to main project dir, not worktree
   (would be deleted in Step 5).
4. "fix these issues" tip only for local reviews — worktree is
   cleaned up after PR review, so interactive fixing not possible.
5. Autofix push uses explicit remote branch name from Step 1.
6. Move incremental check before dependency install to avoid
   wasting time when no new changes.
7. Fix Step 3 reference: "from Steps 2.5 and 2.6" (includes
   reverse audit findings).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

docs/users/features/code-review.md

@@ -98,9 +98,11 @@ Found 3 issues with auto-fixable suggestions. Apply auto-fixes? (y/n)
 When reviewing a PR, `/review` creates a temporary git worktree (`.qwen/tmp/review-pr-<number>`) instead of switching your current branch. This means:
 
 - Your working tree, staged changes, and current branch are **never touched**
+- Dependencies are installed in the worktree (`npm ci`, etc.) so linting and build/test work
 - Build and test commands run in isolation without polluting your local build cache
 - If anything goes wrong, your environment is unaffected — just delete the worktree
 - The worktree is automatically cleaned up after the review completes
+- Review reports and cache are saved to the main project directory (not the worktree)
 
 ## PR Inline Comments