Remove voice_agent scripts, update happy submodule

- Remove voice_agent/ directory (scripts now obsolete, functionality moved to webapp)
- System prompt embedded in happy/sources/sync/apiVoice.ts as single source of truth

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

Author: rrnewton

.beads/issues/hp-18.md

@@ -0,0 +1,20 @@
+---
+title: Add UI support for ElevenLabs integration in Settings
+status: in_progress
+priority: 2
+issue_type: task
+created_at: 2025-12-01T19:46:45.369807850+00:00
+updated_at: 2025-12-01T19:47:43.300297555+00:00
+---
+
+# Description
+
+Currently ElevenLabs config is set via env vars on the server, which assumes single-account usage. Need to move to per-account configuration:
+
+1. Show ELEVENLABS_AGENT_ID and ELEVENLABS_API_KEY in Voice Assistant settings section
+2. Allow users to change these values, persisted to their account
+3. Add toggle: use hardcoded production agent vs custom agent
+4. If production agent toggled off, user must enter their own agent ID and API key
+5. Different accounts should be able to use different agents
+
+This follows the pattern of other connection settings like server URL and GitHub account linking.