Add project scaffolding with fx DI, SQLite migrations, and healthcheck

- go.mod with git.eeqj.de/sneak/chat module
- internal packages: globals, logger, config, db, healthcheck, middleware, handlers, server
- SQLite database with embedded migration system (schema_migrations tracking)
- Migration 001: schema_migrations table
- Migration 002: channels table
- Config with chat-specific vars (MAX_HISTORY, SESSION_TIMEOUT, MAX_MESSAGE_SIZE, MOTD, SERVER_NAME, FEDERATION_KEY)
- Healthcheck endpoint at /.well-known/healthcheck.json
- Makefile, .gitignore
- cmd/chatd/main.go entry point

.gitignore

@@ -0,0 +1,11 @@
+chatd
+data.db
+.env
+*.exe
+*.dll
+*.so
+*.dylib
+*.test
+*.out
+vendor/
+debug.log