Reduce manual verification in checkpoint system (#220)

* docs: enforce automation-first checkpoint verification

Checkpoints should never ask users to run CLI commands that Claude Code
can execute. This update reinforces the automation-first principle:

Key changes:
- Add golden rules: Claude runs CLI, users only visit URLs
- Add dev server automation patterns (start before checkpoint)
- Add environment variable CLI patterns (Convex, Vercel, etc.)
- Add anti-patterns: asking user to run npm, add dashboard env vars
- Update all examples to show Claude starting servers
- Add comprehensive "Never Ask Users To" and "Users Only Do" lists
- Update gsd-executor with pre-checkpoint automation requirements

The core principle: if Claude CAN automate it, Claude MUST automate it.
Users only do what requires human judgment (visual verification, UX).

* refactor: DRY checkpoint automation with server lifecycle and error handling

Changes:
- checkpoints.md is now single source of truth for automation-first patterns
- Added server lifecycle protocol (start, port conflicts, cleanup)
- Added CLI installation handling (auto-install matrix)
- Added pre-checkpoint failure handling (fix before checkpoint)
- Removed ~93 lines of duplication from verification-patterns.md
- Replaced inline examples in phase-prompt.md with references
- Slimmed gsd-executor.md checkpoint section to reference checkpoints.md

Net effect: -23 lines while adding 3 new capabilities (server lifecycle,
CLI install, error handling). Single place to update automation patterns.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

agents/gsd-executor.md

@@ -347,6 +347,21 @@ Type "done" when authenticated.
 </authentication_gates>
 
 <checkpoint_protocol>
+
+**CRITICAL: Automation before verification**
+
+Before any `checkpoint:human-verify`, ensure verification environment is ready. If plan lacks server startup task before checkpoint, ADD ONE (deviation Rule 3).
+
+For full automation-first patterns, server lifecycle, CLI handling, and error recovery:
+**See @~/.claude/get-shit-done/references/checkpoints.md**
+
+**Quick reference:**
+- Users NEVER run CLI commands - Claude does all automation
+- Users ONLY visit URLs, click UI, evaluate visuals, provide secrets
+- Claude starts servers, seeds databases, configures env vars
+
+---
+
 When encountering `type="checkpoint:*"`:
 
 **STOP immediately.** Do not continue to next task.