docs: add Trellis planning and project specs

.trellis/spec/README.md

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+# Next.js Full-Stack Development Guidelines
+
+Universal development guidelines for production Next.js applications with oRPC API layer and PostgreSQL.
+
+## Structure
+
+### [Frontend](./frontend/index.md)
+
+React 19 + Next.js 15 App Router frontend development patterns:
+
+- [Directory Structure](./frontend/directory-structure.md)
+- [Components](./frontend/components.md)
+- [State Management](./frontend/state-management.md)
+- [Hooks](./frontend/hooks.md)
+- [API Integration](./frontend/api-integration.md)
+- [oRPC Usage](./frontend/orpc-usage.md)
+- [Authentication](./frontend/authentication.md)
+- [AI SDK Integration](./frontend/ai-sdk-integration.md)
+- [CSS & Layout](./frontend/css-layout.md)
+- [Type Safety](./frontend/type-safety.md)
+- [Quality Checklist](./frontend/quality.md)
+
+### [Backend](./backend/index.md)
+
+oRPC + Drizzle ORM backend development patterns:
+
+- [Directory Structure](./backend/directory-structure.md)
+- [oRPC Usage](./backend/orpc-usage.md)
+- [Authentication](./backend/authentication.md)
+- [Database](./backend/database.md)
+- [AI SDK Integration](./backend/ai-sdk-integration.md)
+- [Logging](./backend/logging.md)
+- [Performance](./backend/performance.md)
+- [Type Safety](./backend/type-safety.md)
+- [Quality Checklist](./backend/quality.md)
+
+### [Shared](./shared/index.md)
+
+Cross-cutting concerns:
+
+- [Dependencies](./shared/dependencies.md)
+- [Code Quality](./shared/code-quality.md)
+- [TypeScript Conventions](./shared/typescript.md)
+
+### [Guides](./guides/index.md)
+
+Development thinking guides:
+
+- [Pre-Implementation Checklist](./guides/pre-implementation-checklist.md)
+- [Cross-Layer Thinking Guide](./guides/cross-layer-thinking-guide.md)
+
+### [Common Issues / Pitfalls](./big-question/index.md)
+
+Common issues and solutions:
+
+- [PostgreSQL JSON vs JSONB](./big-question/postgres-json-jsonb.md)
+- [WebKit Tap Highlight](./big-question/webkit-tap-highlight.md)
+- [Sentry & next-intl Conflict](./big-question/sentry-nextintl-conflict.md)
+- [Turbopack vs Webpack Flexbox](./big-question/turbopack-webpack-flexbox.md)
+
+## Tech Stack
+
+- **Frontend**: Next.js 15, React 19, TailwindCSS 4, Radix UI, React Query
+- **Backend**: oRPC, Drizzle ORM, PostgreSQL, better-auth
+- **AI**: Vercel AI SDK (multi-provider)
+- **Real-time**: Ably / WebSocket / SSE
+- **Build**: Turborepo + pnpm (monorepo)
+- **Monitoring**: Sentry + OpenTelemetry
+
+## Usage
+
+These guidelines can be used as:
+
+1. **New Project Template** - Copy the entire structure for new Next.js projects
+2. **Reference Documentation** - Consult specific guides when implementing features
+3. **Code Review Checklist** - Verify implementations against established patterns
+4. **Onboarding Material** - Help new developers understand project conventions