Release v1.16.0: install handoff skill, add publish skill, sync upstream

- Make plan2code-handoff an installed workflow prompt: move to src/,
  register in install.js SOURCE_PROMPTS, remove repo-local-only copy
- Add repo-local maintainer /plan2code-publish skill (cuts GitHub Releases;
  excluded from install.js)
- Review workflow next-step suggestion made context-aware (upstream v1.15.4)
- Doc updates: list handoff in README, QUICK-REFERENCE, architecture table;
  add "Adding a New Workflow Prompt / Skill" checklist to dev-commands
- Fix broken AGENTS.md index links: rename .agents-docs loop/metrics files
  to plan2code-* to match references
- Bump version.json to 1.16.0 to align with package.json and CHANGELOG

.agents-docs/AGENTS-plan2code-loop.md

@@ -0,0 +1,47 @@
+# Plan2Code Loop
+> Part of [AGENTS.md](../AGENTS.md) — project guidance for AI coding agents.
+
+A separate Node.js CLI tool that autonomously implements specs by looping through tasks.
+
+## Loop Architecture
+
+The loop uses an **LLM-driven discovery** approach:
+- Node app just orchestrates iterations and parses completion markers
+- The LLM reads spec files (`overview.md`, `phase-X.md`) to discover tasks
+- The LLM finds unchecked checkboxes, implements ONE task per iteration, marks it complete
+- No regex parsing of markdown in Node - the AI handles all task discovery
+
+## Loop Commands
+
+```bash
+# Build the loop CLI
+cd plan2code-loop && npm run build
+
+# Run the loop (after linking) - fully interactive
+plan2code-loop
+```
+
+The CLI auto-detects specs in `./specs/`, prompts for selection if multiple found, and handles session continuation interactively. Session state is stored per-spec in `specs/<feature>/.plan2code-loop/`.
+
+## Loop Modes
+
+The CLI asks users to choose a loop mode:
+- **One task per loop** (default) - Each agent invocation implements exactly one task. The Node controller handles git commits.
+- **One phase per loop** - Each agent invocation implements all remaining tasks in the current phase. The LLM handles git commits (with JIRA ticket ID if provided). The controller parses multiple completion markers from a single iteration.
+
+## Completion Markers
+
+The LLM must output one of these formats:
+- `TASK_COMPLETE: 1.1 - Task description` - Task done successfully
+- `TASK_BLOCKED: 1.1 - Reason` - Cannot complete task
+- `PHASE_COMPLETE` - Current phase finished (phase mode only)
+- `LOOP_COMPLETE` - All phases finished
+
+## Key Source Files
+
+| File | Purpose |
+|------|---------|
+| `plan2code-loop/src/controller.ts` | Main loop orchestrator |
+| `plan2code-loop/src/prompt/templates.ts` | Prompt templates for both loop modes |
+| `plan2code-loop/src/utils/git.ts` | `createTaskCommit()` — handles task-mode commits with footer |
+| `plan2code-loop/src/cli.ts` | Interactive CLI entry point |