feat: add BLOCKED + DIAGNOSE default rule and blocker report template (closes #552)

- Updated llm-project-workflow/SKILL.md with universal BLOCKED + DIAGNOSE rule, covered blocker classes, explicit prohibition of unsafe fallbacks, and proof section.
- Added templates/blocked-diagnose-report.md (standard template with all required fields).
- Updated workflows/work-issue.md, review-merge-pr.md, create-issue.md and templates/start-issue.md, review-pr.md, merge-pr.md, recover-bad-state.md to require and reference the rule at load.
- Updated docs/llm-workflow-runbooks.md to reinforce the rule for controller prompts and all workflows.
- All changes in isolated worktree branches/issue-552-blocked-diagnose. No root mutation. No unsafe fallbacks used.
- Tests (workflow + cleanup proofs): 26+ passed in run.
- git diff --check prgs/master...HEAD: clean.

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

@@ -35,6 +35,7 @@ Load the canonical workflow first:
 Final report schema: `schemas/review-merge-final-report.md`.
 
 Rules (llm-project-workflow):
+- **BLOCKED + DIAGNOSE default (required):** If any required step (load workflow, lease, profile/role, capability, worktree under branches/, preflight, tool, instruction, etc.) cannot be performed, STOP. State BLOCKED. Use [`blocked-diagnose-report.md`](../templates/blocked-diagnose-report.md) template exactly. Only safe non-mutating recovery. Report. Do not continue or fallback.
 - Review in a SEPARATE detached review worktree, never the author's folder.
 - Worktree safety (#233): before checkout, diff, validation, review, or merge,
   report the starting worktree path and whether it was dirty. If unrelated