#20475: fix(macos): resolve 120%+ CPU regression and gateway stability

## Summary - **GatewayChannel CPU fix**: Replace `JSONDecoder` + `AnyCodable` decode with native `JSONSerialization`, eliminating the recursive try/catch cascade that was burning 120%+ CPU on every gateway message. Includes `wrapJSONValue()` helper using `CFBooleanGetTypeID()` to preserve JSON bool/int distinction through NSNumber bridging. - **keepaliveLoop busy-spin fix**: `try? await Task.sleep(...)` silently swallowed `CancellationError`, causing cancelled tasks to spin indefinitely. Now exits cleanly on cancellation. - **TalkOverlayView performance**: Use static `Circle()` when idle/paused instead of 60fps `TimelineView`; throttle active animation to 15fps. - **Duplicate WebSocket prevention**: `DevicePairingApprovalPrompter`, `NodePairingApprovalPrompter`, and `VoiceWakeGlobalSettingsSync` now subscribe to the existing gateway connection instead of calling `refresh()` which spawned duplicate WebSocket connections. - **talk.config systemVoice**: `normalizeTalkConfigSection()` was missing `systemVoice` from its field whitelist, silently dropping it from the response. - **TalkModeRuntime**: Default to Edge TTS (free, no API key) when no ElevenLabs key is configured; system voice only when explicitly requested. Add error logging to `fetchTalkConfig()` catch block. - **Gateway auth**: Allow `health` method for any authenticated role. - **Nextcloud Talk**: Keep channel task alive to prevent framework auto-restart collision. ## Test plan - [ ] Launch macOS app, verify CPU settles below 10% after startup (was 120%+) - [ ] Enter talk mode, verify TTS playback works (Edge TTS default or configured voice) - [ ] Verify gateway WebSocket shows single connection (not duplicates) - [ ] Verify device/node pairing prompts still appear on `device.pair.requested` events - [ ] Verify `talk.config` response includes `systemVoice` when set in config <!-- greptile_comment --> <h3>Greptile Summary</h3> This PR addresses a critical 120%+ CPU regression caused by expensive JSON decoding and implements several gateway stability improvements: - **GatewayChannel CPU fix**: Replaces `JSONDecoder` + `AnyCodable` with native `JSONSerialization` to eliminate recursive try/catch overhead. Includes `wrapJSONValue()` helper using `CFBooleanGetTypeID()` to preserve JSON bool/int distinctions. - **keepaliveLoop busy-spin fix**: Properly handles `CancellationError` instead of silently swallowing it with `try?`, preventing infinite busy-spinning on cancelled tasks. - **TalkOverlayView performance**: Uses static `Circle()` when idle/paused instead of 60fps `TimelineView`, and throttles active animation to 15fps. - **Duplicate WebSocket prevention**: Three components (`DevicePairingApprovalPrompter`, `NodePairingApprovalPrompter`, `VoiceWakeGlobalSettingsSync`) now subscribe to existing gateway connection instead of calling `refresh()`. - **talk.config systemVoice**: Adds missing `systemVoice` field to `normalizeTalkConfigSection()` whitelist. - **Gateway auth**: Allows `health` method for any authenticated role. - **Nextcloud Talk**: Keeps channel task alive to prevent framework auto-restart collision. **Critical Issue**: The PR introduces references to `TalkGatewayTTSSynthesizer` and `TalkSayCommandSynthesizer` classes that don't exist in the codebase, which will cause compilation failures. <h3>Confidence Score: 0/5</h3> - This PR cannot be merged due to missing class definitions that will cause compilation failures - The PR references `TalkGatewayTTSSynthesizer` and `TalkSayCommandSynthesizer` on lines 672-673 and 734-735 of `TalkModeRuntime.swift`, but these classes are not defined anywhere in the codebase. This will cause Swift compilation to fail. While the other changes (CPU fix, keepalive loop, WebSocket deduplication) appear well-implemented and address important issues, the missing synthesizer implementations are blocking issues that must be resolved before merge. - apps/macos/Sources/OpenClaw/TalkModeRuntime.swift requires missing synthesizer implementations _{Last reviewed commit: dde0ce5} <!-- greptile_other_comments_section --> _{(4/5) You can add custom instructions or style guidelines for the agent [here](https://app.greptile.com/review/github)!} <!-- /greptile_comment -->