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>

docs/llm-workflow-runbooks.md

@@ -7,6 +7,12 @@ package of the MCP Control Plane: creating issues, implementing them, opening
 and reviewing pull requests, merging, and closing out — safely and
 reproducibly.
 
+> For the **project-agnostic** version of these operating rules (issue-first,
+> isolated worktrees, no self-review/merge, profile safety, cleanup, fail-closed)
+> that can be copied into any repository, see the reusable skill
+> [`skills/llm-project-workflow/SKILL.md`](../skills/llm-project-workflow/SKILL.md)
+> and its `templates/`. This runbook is the Gitea-specific application of it.
+
 These runbooks are **operational guidance only**. They add no tooling; the
 behavior they rely on already exists (canonical runtime profiles, the
 interactive setup menu, identity/eligibility checks, gated review/merge, and