Add PS_AI_Agent_ElevenLabs plugin (initial implementation)

Adds a new UE5.5 plugin integrating the ElevenLabs Conversational AI Agent
via WebSocket. No gRPC or third-party libs required.

Plugin components:
- UElevenLabsSettings: API key + Agent ID in Project Settings
- UElevenLabsWebSocketProxy: full WS session lifecycle, JSON message handling,
  ping/pong keepalive, Base64 PCM audio send/receive
- UElevenLabsConversationalAgentComponent: ActorComponent for NPC voice
  conversation, orchestrates mic capture -> WS -> procedural audio playback
- UElevenLabsMicrophoneCaptureComponent: wraps Audio::FAudioCapture,
  resamples to 16kHz mono, dispatches on game thread

Also adds .claude/ memory files (project context, plugin notes, patterns)
so Claude Code can restore full context on any machine after a git pull.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

.claude/MEMORY.md

@@ -0,0 +1,35 @@
+# Project Memory – PS_AI_Agent
+
+> This file is committed to the repository so it is available on any machine.
+> Claude Code reads it automatically at session start (via the auto-memory system)
+> when the working directory is inside this repo.
+> **Keep it under ~180 lines** – lines beyond 200 are truncated by the system.
+
+---
+
+## Project Location
+- Repo root: `<repo_root>/` (wherever this is cloned)
+- UE5 project: `<repo_root>/Unreal/PS_AI_Agent/`
+- `.uproject`: `<repo_root>/Unreal/PS_AI_Agent/PS_AI_Agent.uproject`
+- Engine: **Unreal Engine 5.5** — Win64 primary target
+
+## Plugins
+| Plugin | Path | Purpose |
+|--------|------|---------|
+| Convai (reference) | `<repo_root>/ConvAI/Convai/` | gRPC + protobuf streaming to Convai API. Has ElevenLabs voice type enum in `ConvaiDefinitions.h`. Used as architectural reference. |
+| **PS_AI_Agent_ElevenLabs** | `<repo_root>/Unreal/PS_AI_Agent/Plugins/PS_AI_Agent_ElevenLabs/` | Our ElevenLabs Conversational AI integration. See `.claude/elevenlabs_plugin.md` for full details. |
+
+## User Preferences
+- Plugin naming: `PS_AI_Agent_<Service>` (e.g. `PS_AI_Agent_ElevenLabs`)
+- Save memory frequently during long sessions
+- Goal: ElevenLabs Conversational AI integration — simpler than Convai, no gRPC
+- Full original ask + intent: see `.claude/project_context.md`
+
+## Key UE5 Plugin Patterns
+- Settings object: `UCLASS(config=Engine, defaultconfig)` inheriting `UObject`, registered via `ISettingsModule`
+- Module startup: `NewObject<USettings>(..., RF_Standalone)` + `AddToRoot()`
+- WebSocket: `FWebSocketsModule::Get().CreateWebSocket(URL, TEXT(""), Headers)`
+- Audio capture: `Audio::FAudioCapture` from the `AudioCapture` module
+- Procedural audio playback: `USoundWaveProcedural` + `OnSoundWaveProceduralUnderflow` delegate
+- Audio capture callbacks arrive on a **background thread** — always marshal to game thread with `AsyncTask(ENamedThreads::GameThread, ...)`
+- Resample mic audio to **16000 Hz mono** before sending to ElevenLabs