feat: consolidate server-side code into single server/ directory
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>