Add TTS settings for hosted version (open.maic.chat)[Feature]: Add TTS settings for hosted version

## Problem or Motivation

Users of the hosted version (open.maic.chat) cannot configure TTS settings, resulting in **no audio during classroom playback**.

### Current Situation
- Hosted version does not expose TTS provider settings to users
- No settings icon or control bar visible in classroom interface
- Users cannot switch between TTS providers (OpenAI/GLM/Azure/etc.)

### User Report
- Browser: Microsoft Edge
- Classroom URL: https://open.maic.chat/classroom/CBVmiHC-c6
- Issue: No sound when playing classroom content
- No TTS settings accessible

### Expected Behavior
1. **Settings page** at `/settings` should allow TTS provider configuration
2. **Classroom player** should have audio controls
3. **Users should be able to**:
- Select TTS provider (OpenAI/GLM/Azure/Qwen)
- Adjust voice settings
- Enable/disable TTS per classroom

### Suggested Solution

**Option A: Add settings page for hosted version**
- Create `/settings` route for hosted users
- Allow TTS provider selection with user's own API key
- Store preferences in localStorage or user session

**Option B: Add TTS controls in classroom player**
- Add audio control bar at bottom of classroom
- Add settings button in classroom UI
- Allow per-classroom TTS configuration

**Option C: Support user-provided API keys**
- Allow users to input their own TTS API key
- Use user's key instead of server default

### Impact
This affects all users of the hosted version who want audio playback in classrooms. Currently, the hosted version is missing a key feature (TTS) that is available in self-hosted deployments.

### Related Issues
- #145: Browser-native TTS produces broken/garbled audio
- #188: enableTTS description is stale

---

**Environment:**
- Platform: open.maic.chat (hosted version)
- Browser: Microsoft Edge
- Access Code: User has valid access code