docs: add color system architecture and session 48 summary

- Document single source of truth architecture
- Explain CSS variable auto-generation workflow
- Show how colors.mjs eliminates duplication
- Provide maintenance and build integration guide
- Reference commit e715afd8 refactoring

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

dev_docs/SESSION_STATE.md

@@ -264,6 +264,65 @@ Root cause analysis revealed 3 critical failures in DESIGN.md compliance:
 
 ---
 
+## SESSION 48 EXECUTION SUMMARY — Architectural Refactoring: Single Source of Truth
+
+### Identified Issue
+User question: "Are both tailwind.config.ts and globals.css necessary? If any color needs to be changed, the same information is hardcoded in two different files."
+- **Root Problem**: Color definitions duplicated in 2 places (DRY violation)
+- **Impact**: Any color change requires editing in 2 files
+- **Risk**: Easy to update one file and forget the other, causing sync issues
+
+### Solution: Option 1 - Single Source of Truth
+Implemented consolidated color architecture with 3 files:
+
+1. **frontend/colors.mjs** (NEW - SINGLE SOURCE OF TRUTH)
+   - Exports `colors` object with all 40+ design system colors
+   - Exports `spacing` object with all semantic spacing tokens
+   - Machine-readable, importable format
+   - Comment clearly states: "Changes here automatically propagate to both files"
+
+2. **frontend/scripts/generate-css-vars.mjs** (NEW - BUILD STEP)
+   - Reads colors.mjs as input
+   - Auto-generates CSS custom properties (--primary, --secondary, etc.)
+   - Injects generated variables into globals.css :root section
+   - Runs on every build (dev and production)
+   - Prevents manual sync issues
+
+3. **frontend/tailwind.config.ts** (UPDATED)
+   - Now imports colors from colors.mjs
+   - Line 17: `import { colors as colorsDefinition } from "./colors.mjs";`
+   - Line 58: `colors: colorsDefinition,` (single source reference)
+   - Eliminated 80+ lines of duplicated color definitions
+
+### Build System Integration
+**frontend/package.json** (UPDATED)
+- Added script: `"generate-css-vars": "node scripts/generate-css-vars.mjs"`
+- Updated `"dev"`: now runs `npm run generate-css-vars && next dev`
+- Updated `"build"`: now runs `npm run generate-css-vars && next build`
+
+**start_servers.py** (UPDATED)
+- Added build step in `setup_frontend()` method
+- Runs `node scripts/generate-css-vars.mjs` before `npm run build`
+- Ensures CSS variables are synchronized before every build
+
+### Verification
+✅ CSS variable generation script tested and working
+✅ Build process succeeds with 0 errors (5.7s compile time)
+✅ All pages generated (8/8)
+✅ No CSS or TypeScript warnings
+✅ Commit: e715afd8 - "refactor: consolidate color definitions into single source of truth"
+
+### Benefits Delivered
+| Metric | Before | After |
+|--------|--------|-------|
+| Color definition locations | 2 (duplicated) | 1 (colors.mjs) |
+| Lines of duplicate code | 80+ | 0 |
+| Build complexity | Manual sync | Automated |
+| Update effort | 2 files | 1 file |
+| Sync risk | High | None |
+
+---
+
 ## NEXT STEPS (Phase 11: Visual Testing & Version Bump)
 
 1. **Visual Verification (RECOMMENDED):**