feat: Migrate from agent markdown files to Skills, Rules, and Sub-Agents

Replace the manual "read .claude/agents/*.md" workflow with native
Claude Code features for a more efficient, scalable development experience:

- **Skills** (.claude/skills/): 7 auto-discovered slash commands
  (/requirements, /architecture, /frontend, /backend, /qa, /deploy, /help)
  with forked sub-agents for heavy tasks and inline execution for interactive ones
- **Rules** (.claude/rules/): 4 modular rule files (general, frontend, backend,
  security) auto-applied based on file context
- **Sub-Agents** (.claude/agents/): Lightweight configs for frontend-dev,
  backend-dev, and qa-engineer with model, tool, and turn limit settings
- **Context Engineering**: Layered context loading, context isolation via
  forked skills, built-in context recovery after compaction, and
  "always read, never guess" rules to prevent hallucinated code references
- **CLAUDE.md**: Auto-loaded project context replacing PROJECT_CONTEXT.md
- **Feature tracking**: features/INDEX.md as persistent state across sessions
- **Production guides**: docs/production/ for error tracking, security,
  performance, database optimization, and rate limiting
- **Init Mode**: /requirements detects empty PRD and bootstraps full project
  setup (PRD + all feature specs) from a single project description

Removed: 6 monolithic agent files, PROJECT_CONTEXT.md, HOW_TO_USE_AGENTS.md,
TEMPLATE_CHANGELOG.md

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

docs/production/error-tracking.md

@@ -0,0 +1,43 @@
+# Error Tracking Setup (Sentry)
+
+Track production errors automatically so you know about issues before your users report them.
+
+## Setup (5 minutes)
+
+### 1. Create Sentry Account
+- Go to [sentry.io](https://sentry.io) (free tier available for small apps)
+- Create a new project and select "Next.js"
+
+### 2. Install Next.js Integration
+```bash
+npx @sentry/wizard@latest -i nextjs
+```
+This automatically:
+- Installs `@sentry/nextjs`
+- Creates `sentry.client.config.ts` and `sentry.server.config.ts`
+- Updates `next.config.ts` with Sentry webpack plugin
+
+### 3. Add Environment Variables
+Add to `.env.local` (local) and Vercel Dashboard (production):
+```bash
+SENTRY_DSN=https://xxx@xxx.ingest.sentry.io/xxx
+NEXT_PUBLIC_SENTRY_DSN=https://xxx@xxx.ingest.sentry.io/xxx
+SENTRY_AUTH_TOKEN=sntrys_xxx  # For source maps upload
+```
+
+### 4. Verify Setup
+Trigger a test error and check Sentry Dashboard:
+```typescript
+// Temporary test - remove after verification
+throw new Error("Sentry test error")
+```
+
+## What You Get
+- Automatic error capture (client + server)
+- Stack traces with source maps
+- Error grouping and deduplication
+- Email alerts for new errors
+- Performance monitoring (optional)
+
+## Alternative
+**Vercel Error Tracking** - Built-in, simpler, but fewer features. Available in Vercel Dashboard under "Monitoring".