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/start-issue.md

@@ -0,0 +1,29 @@
+# Template: start a new issue
+
+Copy, fill the `<...>` fields, and paste as the task prompt.
+
+```text
+Task: implement <issue title / one-line goal>.
+
+Rules (llm-project-workflow):
+- No repo changes without a tracking issue. If none exists, create one first;
+  if it can't be created, stop.
+- Work only in an isolated branch worktree under branches/. The main checkout
+  is orchestration/status only.
+- Do not self-review or self-merge.
+
+Steps:
+1. Verify the orchestration checkout is the right repo and clean.
+2. git fetch <remote> --prune; confirm local master == <remote>/master (0 0).
+3. Create the issue "<title>" (problem, scope, acceptance) and claim it
+   (status:in-progress + a "starting work" comment naming the branch).
+4. scripts/worktree-start <type>/issue-<n>-<slug>   # type = fix|feat|docs
+   cd branches/<type>-issue-<n>-<slug>
+5. Implement the narrow scope only; add/update focused tests if behavior changes.
+6. Checks: run the test suite, compile/lint changed files, git diff --check,
+   and scan the diff for secrets.
+7. Commit (issue-linked message), push the branch, open a PR to master.
+8. Stop before review/merge — you are the author.
+
+Handoff: issue #, branch, worktree path, files changed, checks + results, PR URL.
+```