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/LEGAL.md

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+# Legal Notice
+
+## Disclaimer
+
+This project is an unofficial, community-maintained SDK for building extensions
+for [Antigravity IDE](https://antigravity.dev). It is **not affiliated with,
+endorsed by, or sponsored by Google LLC or any of its subsidiaries.**
+
+## Nature of the Project
+
+Antigravity SDK provides a **TypeScript library** for VS Code extension
+developers who want to build tools that work within Antigravity IDE.
+
+The SDK interacts with Antigravity exclusively through:
+
+- **VS Code Extension API** — the standard, documented `vscode.*` namespace
+  that all extensions use
+- **Registered commands** — commands exposed by Antigravity through the
+  standard `vscode.commands` interface
+- **Local state files** — reading (not writing) locally stored settings
+
+## Compliance
+
+- This SDK **does not access** Google's backend servers, gRPC endpoints,
+  or authentication systems directly.
+- This SDK **does not extract** AI models, training data, weights, or
+  proprietary algorithms.
+- This SDK **does not bypass** security features, licensing, rate limits,
+  or usage restrictions.
+- This SDK **does not proxy** or relay requests to Google's infrastructure.
+- All communication goes through Antigravity's own extension host — the same
+  mechanism used by any VS Code extension.
+
+## Interoperability
+
+This SDK is developed to enable interoperability between Antigravity IDE
+and third-party extensions, as provided by:
+
+- **EU Software Directive** (Directive 2009/24/EC), Article 6 — permits
+  analysis of software for the purpose of achieving interoperability
+- **UK Copyright, Designs and Patents Act 1988**, Section 50B
+- Similar provisions in other jurisdictions
+
+The API interfaces documented in this project were derived through observation
+of Antigravity's public extension API surface — the same surface available to
+any VS Code extension running inside Antigravity.
+
+## User Responsibility
+
+Users and extension developers are responsible for ensuring their use of
+this SDK and any extensions built with it comply with applicable terms of
+service and local laws.
+
+Extension developers should:
+
+1. Not use the SDK to access Google's backend directly
+2. Not use the SDK to extract or replicate AI model behavior
+3. Not use the SDK to bypass security or licensing restrictions
+4. Follow Antigravity's extension guidelines where applicable
+
+## Takedown
+
+If Google or the Antigravity team requests removal of this project, we will
+comply promptly. Contact: [open a GitHub issue](https://github.com/Kanezal/antigravity-sdk/issues).
+
+## License
+
+This project is released under the [GNU Affero General Public License v3.0](LICENSE).