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>

CLAUDE.md

@@ -0,0 +1,66 @@
+# AI Coding Starter Kit
+
+> A Next.js template with an AI-powered development workflow using specialized skills for Requirements, Architecture, Frontend, Backend, QA, and Deployment.
+
+## Tech Stack
+
+- **Framework:** Next.js 16 (App Router), TypeScript
+- **Styling:** Tailwind CSS + shadcn/ui (copy-paste components)
+- **Backend:** Supabase (PostgreSQL + Auth + Storage) - optional
+- **Deployment:** Vercel
+- **Validation:** Zod + react-hook-form
+- **State:** React useState / Context API
+
+## Project Structure
+
+```
+src/
+  app/              Pages (Next.js App Router)
+  components/
+    ui/             shadcn/ui components (NEVER recreate these)
+  hooks/            Custom React hooks
+  lib/              Utilities (supabase.ts, utils.ts)
+features/           Feature specifications (PROJ-X-name.md)
+  INDEX.md          Feature status overview
+docs/
+  PRD.md            Product Requirements Document
+  production/       Production guides (Sentry, security, performance)
+```
+
+## Development Workflow
+
+1. `/requirements` - Create feature spec from idea
+2. `/architecture` - Design tech architecture (PM-friendly, no code)
+3. `/frontend` - Build UI components (shadcn/ui first!)
+4. `/backend` - Build APIs, database, RLS policies
+5. `/qa` - Test against acceptance criteria + security audit
+6. `/deploy` - Deploy to Vercel + production-ready checks
+
+## Feature Tracking
+
+All features tracked in `features/INDEX.md`. Every skill reads it at start and updates it when done. Feature specs live in `features/PROJ-X-name.md`.
+
+## Key Conventions
+
+- **Feature IDs:** PROJ-1, PROJ-2, etc. (sequential)
+- **Commits:** `feat(PROJ-X): description`, `fix(PROJ-X): description`
+- **Single Responsibility:** One feature per spec file
+- **shadcn/ui first:** NEVER create custom versions of installed shadcn components
+- **Human-in-the-loop:** All workflows have user approval checkpoints
+
+## Build & Test Commands
+
+```bash
+npm run dev        # Development server (localhost:3000)
+npm run build      # Production build
+npm run lint       # ESLint
+npm run start      # Production server
+```
+
+## Product Context
+
+@docs/PRD.md
+
+## Feature Overview
+
+@features/INDEX.md