feat: /gsd:ship command for PR creation from verified phase work (#829) (#1123)

* feat: /gsd:ship command for PR creation from verified phase work (#829)

New command that bridges local completion → merged PR, closing the
plan → execute → verify → ship loop.

Workflow (workflows/ship.md):
1. Preflight: verification passed, clean tree, correct branch, gh auth
2. Push branch to remote
3. Auto-generate rich PR body from planning artifacts:
   - Phase goal from ROADMAP.md
   - Changes from SUMMARY.md files
   - Requirements addressed (REQ-IDs)
   - Verification status
   - Key decisions
4. Create PR via gh CLI (supports --draft)
5. Optional code review request
6. Update STATE.md with shipping status

Files:
- commands/gsd/ship.md: New command entry point
- get-shit-done/workflows/ship.md: Full workflow implementation
- get-shit-done/workflows/help.md: Add ship to help output
- docs/COMMANDS.md: Command reference
- docs/FEATURES.md: Feature spec with REQ-SHIP-01 through 05
- docs/USER-GUIDE.md: Add to command table
- CHANGELOG.md: Document new command

Fixes #829

* fix(tests): update expected skill count from 39 to 40 for new ship command

The Copilot install E2E tests hardcode the expected number of skill
directories and manifest entries. Adding commands/gsd/ship.md increased
the count from 39 to 40.

docs/COMMANDS.md

@@ -132,6 +132,32 @@ User acceptance testing with auto-diagnosis.
 
 ---
 
+### `/gsd:ship`
+
+Create PR from completed phase work with auto-generated body.
+
+| Argument | Required | Description |
+|----------|----------|-------------|
+| `N` | No | Phase number or milestone version (e.g., `4` or `v1.0`) |
+| `--draft` | No | Create as draft PR |
+
+**Prerequisites:** Phase verified (`/gsd:verify-work` passed), `gh` CLI installed and authenticated
+**Produces:** GitHub PR with rich body from planning artifacts, STATE.md updated
+
+```bash
+/gsd:ship 4                         # Ship phase 4
+/gsd:ship 4 --draft                 # Ship as draft PR
+```
+
+**PR body includes:**
+- Phase goal from ROADMAP.md
+- Changes summary from SUMMARY.md files
+- Requirements addressed (REQ-IDs)
+- Verification status
+- Key decisions
+
+---
+
 ### `/gsd:ui-review`
 
 Retroactive 6-pillar visual audit of implemented frontend.