fix(bridge): rawRPC direct polling + SDK analysis docs + trial-and-error log

- Root cause: getDiagnostics.lastStepIndex is stale, SDK EventMonitor cannot detect real-time step changes
- Fix: Direct rawRPC('GetCascadeTrajectorySteps') polling every 5s
- Relay: PLANNER_RESPONSE, NOTIFY_USER, TASK_BOUNDARY, WAITING steps
- Added: docs/discord-bridge-analysis.md (full SDK architecture analysis)
- Added: docs/devlog/entries/20260308-003.md (trial-and-error history)
- Added: antigravity-sdk-main/ source reference
- Vikunja: #252 done, #253 created, #251 commented

antigravity-sdk-main/src/core/index.ts

@@ -0,0 +1,11 @@
+/**
+ * Core module — types, events, disposables, errors, logging.
+ *
+ * @module core
+ */
+
+export * from './types';
+export * from './events';
+export * from './disposable';
+export * from './errors';
+export { Logger, LogLevel } from './logger';