docs: add portable llm-project-workflow skill + templates (#46)

Extract the project's operating rules into a reusable, project-agnostic skill
so any repo can adopt the same safe LLM workflow.

- skills/llm-project-workflow/SKILL.md: issue-first; isolated branch worktrees
  (main checkout = orchestration only); distinct author/reviewer identities and
  profile safety (secrets by reference only; stop if authenticated user == PR
  author); branch naming; start/review/merge/cleanup workflows; fail-closed
  cases; recovery patterns; and an "Adapting to a project" table for the
  forge-specific names.
- templates/: copy/paste prompts for start-issue, review-pr, merge-pr,
  recover-bad-state, worktree-cleanup.
- Link the skill from README.md and docs/llm-workflow-runbooks.md (the runbook
  is framed as the Gitea-specific application of the portable skill).

Docs-only; no code, no secrets, safe placeholder examples only. No change to
MCP runtime, Gitea API, credential storage, or worktree helpers.

Checks: full suite 287 passed / 0 failures; git diff --check clean; secret scan
of skills/ clean.

Closes #46. Refs #38, #39.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

skills/llm-project-workflow/templates/merge-pr.md

@@ -1,43 +1,28 @@
-# Merge PR Prompt
+# Template: merge a PR (eligible reviewer only)
 
-You are the merge operator for PR `<pr-number>` in `<repo-name>`.
+Copy, fill the `<...>` fields, and paste as the task prompt.
 
-Hard gate:
+```text
+Task: merge PR #<pr> for issue #<n> if it is eligible and checks pass.
 
-- Verify authenticated identity before reviewing or merging.
-- Verify PR author.
-- If authenticated user matches the PR author, stop immediately.
-- Merge only if assigned merge duty and reviewer-eligible.
+Rules (llm-project-workflow):
+- Only an eligible, NON-author reviewer merges. If authenticated user == PR
+  author → STOP.
+- Do not merge unless the PR is open, mergeable, and its checks/review pass.
+- No force-merge, no bypassing branch protections.
 
-Workflow:
+Steps:
+1. Verify authenticated identity + active profile.
+2. Confirm PR #<pr>: author (not you), state open, mergeable, review approved.
+3. If any gate fails → STOP and report.
+4. Merge with explicit confirmation (e.g. confirmation="MERGE PR <pr>"),
+   optionally pinning the reviewed head SHA / changed-file set.
+5. Confirm remote master now contains the merge commit.
 
-1. Confirm PR `<pr-number>` is open and targets `<default-branch>`.
-2. Confirm the PR head is still `<reviewed-commit>` or includes it.
-3. Confirm changed files still match the reviewed file list.
-4. Confirm previous validation still applies or rerun required checks.
-5. Merge through the gated project merge workflow.
-6. Confirm remote `<default-branch>` contains the merge.
-7. Close or release linked issue `<issue-number>` according to project policy.
-8. Remove `status:in-progress` if applicable.
-9. Delete the merged remote branch if policy allows.
-10. Remove local PR branch and branch worktree only after merge is confirmed.
-11. Fetch/prune.
-12. Confirm main checkout is clean/current.
+Then run the cleanup template (worktree-cleanup.md):
+- close/release issue #<n>, remove status:in-progress
+- delete remote branch, remove local branch + worktree folder
+- fetch/prune; confirm main checkout is clean and current (0 0).
 
-Stop if:
-
-- authenticated user is the PR author
-- PR head changed after review
-- PR is closed but not merged
-- tests/checks fail
-- cleanup would delete unmerged work
-
-Report:
-
-- authenticated user
-- PR author
-- eligibility result
-- merge commit/hash
-- issue final state
-- branch/worktree cleanup result
-- final PR URL
+Handoff: reviewer identity, merge result + commit, cleanup done, issue closed.
+```