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/tsup.config.ts

@@ -0,0 +1,12 @@
+import { defineConfig } from 'tsup';
+
+export default defineConfig({
+    entry: ['src/index.ts'],
+    format: ['cjs'],
+    dts: true,
+    sourcemap: true,
+    clean: true,
+    external: ['vscode'],
+    splitting: false,
+    treeshake: true,
+});