feat: code-aware discuss phase with codebase scouting (#727)

Add lightweight codebase scanning before gray area identification:
- New scout_codebase step checks for existing maps or does targeted grep
- Gray areas annotated with code context (existing components, patterns)
- Discussion options informed by what already exists in the codebase
- Context7 integration for library-specific questions
- CONTEXT.md template includes code_context section

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

commands/gsd/discuss-phase.md

@@ -10,6 +10,8 @@ allowed-tools:
   - Grep
   - AskUserQuestion
   - Task
+  - mcp__context7__resolve-library-id
+  - mcp__context7__query-docs
 ---
 
 <objective>
@@ -38,11 +40,12 @@ Context files are resolved in-workflow using `init phase-op` and roadmap/state t
 <process>
 1. Validate phase number (error if missing or not in roadmap)
 2. Check if CONTEXT.md exists (offer update/view/skip if yes)
-3. **Analyze phase** — Identify domain and generate phase-specific gray areas
-4. **Present gray areas** — Multi-select: which to discuss? (NO skip option)
-5. **Deep-dive each area** — 4 questions per area, then offer more/next
-6. **Write CONTEXT.md** — Sections match areas discussed
-7. Offer next steps (research or plan)
+3. **Scout codebase** — Find reusable assets, patterns, and integration points
+4. **Analyze phase** — Identify domain and generate code-informed gray areas
+5. **Present gray areas** — Multi-select: which to discuss? (NO skip option)
+6. **Deep-dive each area** — 4 questions per area, code-informed options, Context7 for library choices
+7. **Write CONTEXT.md** — Sections match areas discussed + code_context section
+8. Offer next steps (research or plan)
 
 **CRITICAL: Scope guardrail**
 - Phase boundary from ROADMAP.md is FIXED