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/schemas/reconcile-landed-final-report.md

@@ -0,0 +1,53 @@
+# Reconcile-landed controller handoff schema
+
+**Task mode:** `reconcile-landed-pr`
+
+End every reconciliation run with a section titled exactly `Controller Handoff`.
+Use this canonical field set. Do not omit fields — use `none` or
+`not verified in this session` where appropriate.
+
+Reject stale author/reviewer fields: `PR number opened`, `Pinned reviewed head`,
+`Scratch worktree used`, `Workspace mutations`, `Mutations: None` (when mutations
+occurred).
+
+```md
+## Controller Handoff
+
+- Task:
+- Repo:
+- Role:
+- Identity:
+- Active profile:
+- Runtime context:
+- Selected PR:
+- PR live state:
+- Candidate head SHA:
+- Target branch:
+- Target branch SHA:
+- Ancestor proof:
+- Linked issue:
+- Linked issue live status:
+- Eligibility class:
+- Capabilities proven:
+- Missing capabilities:
+- PR comments posted:
+- Issue comments posted:
+- PRs closed:
+- Issues closed:
+- File edits by reconciler:
+- Worktree/index mutations:
+- Git ref mutations:
+- MCP/Gitea mutations:
+- Reconciliation mutations:
+- External-state mutations:
+- Read-only diagnostics:
+- Blockers:
+- Current status:
+- Safe next action:
+- Safety statement:
+- No review/merge confirmation:
+```
+
+Identity format: `username / profile` (not personal email unless required — #305).
+
+`git fetch` belongs under `Git ref mutations`, not read-only diagnostics (#297).