docs: rewrite docs as feature-oriented site (#2163)

Author: koistya

AGENTS.md

@@ -25,7 +25,7 @@
 ```bash
 bun dev                        # Start web + api + app concurrently
 bun build                      # Build email → web → api → app (in order)
-bun test                       # Vitest (single run, not watch)
+bun test                       # Vitest (watch mode; --run for single run)
 bun lint                       # ESLint with cache
 bun typecheck                  # tsc --build
 bun ui:add <component>         # Add shadcn/ui component to packages/ui

README.md

@@ -2,6 +2,7 @@
 
 # React Starter Kit
 
+<a href="https://reactstarter.com/getting-started/"><img src="https://img.shields.io/badge/Docs-007ec6" height="20"></a>
 <a href="https://github.com/kriasoft/react-starter-kit?sponsor=1"><img src="https://img.shields.io/badge/-GitHub-%23555.svg?logo=github-sponsors" height="20"></a>
 <a href="https://discord.gg/2nKEnKq"><img src="https://img.shields.io/discord/643523529131950086?label=Chat" height="20"></a>
 <a href="https://chatgpt.com/g/g-69564f0a23088191846aa4072bd9397d-react-starter-kit-assistant"><img src="https://img.shields.io/badge/Ask_ChatGPT-10a37f?logo=openai&logoColor=white" height="20"></a>
@@ -179,6 +180,8 @@ bun app:deploy     # Deploy main React app
 
 ## Need Help?
 
+**[Documentation](https://reactstarter.com/)** covers auth, database, billing, deployment, and more.
+
 Our AI assistant is trained on this codebase — ask it anything on [ChatGPT](https://chatgpt.com/g/g-69564f0a23088191846aa4072bd9397d-react-starter-kit-assistant) or [Gemini](https://gemini.google.com/gem/1IXFElQ2UvvZY86iL6uZLeoC-r8mp-OB-?usp=sharing). Try these questions:
 
 - [How do I add a new tRPC endpoint?](https://chatgpt.com/g/g-69564f0a23088191846aa4072bd9397d-react-starter-kit-assistant?prompt=How%20do%20I%20add%20a%20new%20tRPC%20endpoint%3F)

apps/api/AGENTS.md

@@ -26,7 +26,7 @@
 ## Request Context
 
 - `ctx.cache: Map<string | symbol, unknown>` — request-scoped cache.
-- DataLoaders use Symbol keys to avoid collisions. Pattern: check `cache.has()`, create loader on miss, return typed cast.
+- DataLoaders use `defineLoader(symbol, batchFn)` helper — handles cache check, instance creation, and typing. See `lib/loaders.ts`.
 - AI provider instances (OpenAI) also cached per-request via same pattern.
 
 ## Environment