docs: split LLM project workflow into task-specific modes (Closes #333)

Consolidate all four canonical workflow files and router SKILL.md:
- review-merge-pr.md (from #334 canonical prompt)
- reconcile-landed-pr.md (reconciliation gates + handoff schema)
- create-issue.md (canonical issue-creation prompt)
- work-issue.md (canonical author/coder prompt)

SKILL.md is now a short router with mode isolation and universal rules.
Adds final-report schemas for all modes and 13 doc-contract tests.

Supersedes partial split work in PR #335; full #333 acceptance in one PR.

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

@@ -5,6 +5,10 @@ Copy, fill the `<...>` fields, and paste as the task prompt.
 ```text
 Task: merge PR #<pr> for issue #<n> if it is eligible and checks pass.
 
+Load the canonical workflow first:
+`skills/llm-project-workflow/workflows/review-merge-pr.md` (task mode: review-merge-pr).
+Final report schema: `schemas/review-merge-final-report.md`.
+
 Rules (llm-project-workflow):
 - Only an eligible, NON-author reviewer merges. If authenticated user == PR
   author → STOP.

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

@@ -30,6 +30,10 @@ Repo name disambiguation (Gitea-Tools blind review hardening):
   commit is not valid corroboration. Author-bound sessions must not present
   reviewer queue inventory as a reviewer decision.
 
+Load the canonical workflow first:
+`skills/llm-project-workflow/workflows/review-merge-pr.md` (task mode: review-merge-pr).
+Final report schema: `schemas/review-merge-final-report.md`.
+
 Rules (llm-project-workflow):
 - Review in a SEPARATE detached review worktree, never the author's folder.
 - Worktree safety (#233): before checkout, diff, validation, review, or merge,

skills/llm-project-workflow/templates/start-issue.md

@@ -5,8 +5,9 @@ Copy, fill the `<...>` fields, and paste as the task prompt.
 ```text
 Task: implement <issue title / one-line goal>.
 
-Canonical workflow: skills/llm-project-workflow/workflows/work-issue.md
+Load canonical workflow: skills/llm-project-workflow/workflows/work-issue.md
 Final report schema: skills/llm-project-workflow/schemas/work-issue-final-report.md
+Router: skills/llm-project-workflow/SKILL.md (task mode: work-issue)
 
 Rules (llm-project-workflow):
 - No repo changes without a tracking issue. If none exists, create one first;