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

Rewrite server.ts to Request→Response handler, add SSR renderer and
Node.js adapter, implement session cookies for viewer resolution in
SSR, add /__dev/login endpoint for test auth, register core XRPC
handlers for preferences, fix OAuth scope joining, switch test context
to SQLite, and add /__dev/ route forwarding in vite plugin.

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

Add define functions (defineFeed, defineQuery, defineProcedure, defineSetup,
defineHook, defineLabels, defineOG) with __type discriminants. Add recursive
scanner that discovers and categorizes server/ modules by type. Add
server-init.ts that wires scanner results to registration functions. Update
main.ts to use initServer() when server/ directory exists, with fallback to
legacy separate directories. Update codegen to scaffold server/ files and
export all define functions from hatk.generated.ts.

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