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/FEATURES.md

@@ -261,6 +261,25 @@
 
 ---
 
+### 6.5. Ship
+
+**Command:** `/gsd:ship [N] [--draft]`
+
+**Purpose:** Bridge local completion → merged PR. After verification passes, push branch, create PR with auto-generated body from planning artifacts, optionally trigger review, and track in STATE.md.
+
+**Requirements:**
+- REQ-SHIP-01: System MUST verify phase has passed verification before shipping
+- REQ-SHIP-02: System MUST push branch and create PR via `gh` CLI
+- REQ-SHIP-03: System MUST auto-generate PR body from SUMMARY.md, VERIFICATION.md, and REQUIREMENTS.md
+- REQ-SHIP-04: System MUST update STATE.md with shipping status and PR number
+- REQ-SHIP-05: System MUST support `--draft` flag for draft PRs
+
+**Prerequisites:** Phase verified, `gh` CLI installed and authenticated, work on feature branch
+
+**Produces:** GitHub PR with rich body, STATE.md updated
+
+---
+
 ### 7. UI Review
 
 **Command:** `/gsd:ui-review [N]`