feat(health): add /gsd:health command for planning directory validation

Validates .planning/ integrity and reports actionable issues:
- Missing/malformed files (PROJECT.md, ROADMAP.md, STATE.md, config.json)
- Phase directory naming, orphaned plans, roadmap/disk consistency
- Auto-repair for config.json and STATE.md with --repair flag

Closes #338

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

commands/gsd/health.md

@@ -0,0 +1,22 @@
+---
+name: gsd:health
+description: Diagnose planning directory health and optionally repair issues
+argument-hint: [--repair]
+allowed-tools:
+  - Read
+  - Bash
+  - Write
+  - AskUserQuestion
+---
+<objective>
+Validate `.planning/` directory integrity and report actionable issues. Checks for missing files, invalid configurations, inconsistent state, and orphaned plans.
+</objective>
+
+<execution_context>
+@~/.claude/get-shit-done/workflows/health.md
+</execution_context>
+
+<process>
+Execute the health workflow from @~/.claude/get-shit-done/workflows/health.md end-to-end.
+Parse --repair flag from arguments and pass to workflow.
+</process>