feat: add /gsd:debug for systematic debugging with persistent state

- Creates .planning/debug/[slug].md immediately on command
- Continuous updates: file IS the debugging brain
- Clear section rules: OVERWRITE (Current Focus, Resolution) vs APPEND (Evidence, Eliminated)
- Survives /clear perfectly - resume from any interruption point
- Scientific method: evidence → hypothesis → test → eliminate or confirm
- Includes debugging reference files (mindset, hypothesis testing, investigation techniques)

Closes #53, closes #44

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

commands/gsd/debug.md

@@ -0,0 +1,58 @@
+---
+name: gsd:debug
+description: Systematic debugging with persistent state across context resets
+argument-hint: [issue description]
+allowed-tools:
+  - Read
+  - Write
+  - Edit
+  - Bash
+  - Grep
+  - Glob
+  - AskUserQuestion
+---
+
+<objective>
+Debug issues using scientific method with a persistent debug document that survives `/clear`.
+
+If resuming (no arguments and active session exists): pick up where you left off.
+If starting new: gather symptoms, then investigate autonomously.
+</objective>
+
+<execution_context>
+@~/.claude/get-shit-done/workflows/debug.md
+@~/.claude/get-shit-done/templates/DEBUG.md
+</execution_context>
+
+<context>
+User's issue: $ARGUMENTS
+
+Check for active debug sessions:
+```bash
+ls .planning/debug/*.md 2>/dev/null | head -5
+```
+</context>
+
+<process>
+Follow the workflow in @~/.claude/get-shit-done/workflows/debug.md
+
+**Quick reference:**
+
+1. **Check for active sessions** - Offer to resume or start new
+2. **Gather symptoms** - What happened? What should happen? Errors? When?
+3. **Create DEBUG.md** - Document symptoms in `.planning/debug/[slug].md`
+4. **Investigate** - Evidence → Hypothesis → Test → Eliminate or Confirm
+5. **Fix and verify** - Minimal fix, verify against original symptoms
+6. **Archive** - Move to `.planning/debug/resolved/`
+
+**Key principle:** The DEBUG.md is your memory. Update it constantly. It survives `/clear`.
+</process>
+
+<success_criteria>
+- [ ] Active sessions checked before starting new
+- [ ] Symptoms gathered through AskUserQuestion (not inline questions)
+- [ ] DEBUG.md tracks all investigation state
+- [ ] Scientific method followed (not random fixes)
+- [ ] Root cause confirmed with evidence before fixing
+- [ ] Fix verified and session archived
+</success_criteria>