feat: enhance roadmap and planning workflows

- create-roadmap: improved phase structuring and requirements tracing
- plan-phase: better task decomposition and wave assignment
- roadmap.md template: cleaner format
- phase-prompt.md template: structured planning prompt

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

commands/gsd/create-roadmap.md

@@ -22,6 +22,7 @@ Run after `/gsd:define-requirements`.
 @~/.claude/get-shit-done/workflows/create-roadmap.md
 @~/.claude/get-shit-done/templates/roadmap.md
 @~/.claude/get-shit-done/templates/state.md
+@~/.claude/get-shit-done/references/goal-backward.md
 </execution_context>
 
 <context>
@@ -121,7 +122,9 @@ Roadmap created:
 - [ ] PROJECT.md validated
 - [ ] REQUIREMENTS.md validated
 - [ ] All v1 requirements mapped to phases (no orphans)
-- [ ] ROADMAP.md created with phases and requirement mappings
+- [ ] Success criteria derived for each phase (2-5 observable behaviors)
+- [ ] Success criteria cross-checked against requirements (gaps resolved)
+- [ ] ROADMAP.md created with phases, requirement mappings, and success criteria
 - [ ] STATE.md initialized
 - [ ] REQUIREMENTS.md traceability section updated
 - [ ] Phase directories created

commands/gsd/plan-phase.md

@@ -28,6 +28,7 @@ Output: One or more PLAN.md files in the phase directory (.planning/phases/XX-na
 @~/.claude/get-shit-done/references/scope-estimation.md
 @~/.claude/get-shit-done/references/checkpoints.md
 @~/.claude/get-shit-done/references/tdd.md
+@~/.claude/get-shit-done/references/goal-backward.md
 </execution_context>
 
 <context>
@@ -77,6 +78,7 @@ Check for `.planning/codebase/` and load relevant documents based on phase type.
 
 - One or more PLAN.md files created in .planning/phases/XX-name/
 - Each plan has: objective, execution_context, context, tasks, verification, success_criteria, output
+- must_haves derived from phase goal and documented in frontmatter (truths, artifacts, key_links)
 - Tasks are specific enough for Claude to execute
 - User knows next steps (execute plan or review/adjust)
   </success_criteria>