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.

get-shit-done/workflows/help.md

@@ -308,6 +308,20 @@ Validate built features through conversational UAT.
 
 Usage: `/gsd:verify-work 3`
 
+### Ship Work
+
+**`/gsd:ship [phase]`**
+Create a PR from completed phase work with an auto-generated body.
+
+- Pushes branch to remote
+- Creates PR with summary from SUMMARY.md, VERIFICATION.md, REQUIREMENTS.md
+- Optionally requests code review
+- Updates STATE.md with shipping status
+
+Prerequisites: Phase verified, `gh` CLI installed and authenticated.
+
+Usage: `/gsd:ship 4` or `/gsd:ship 4 --draft`
+
 ### Milestone Auditing
 
 **`/gsd:audit-milestone [version]`**