HDMI-CEC: auto-disable in dev mode + docs/tests synced

README: document dev-mode CEC auto-disable; add testing notes; set CEC_POWER_OFF_WAIT=5
Copilot instructions: add dev-mode CEC behavior and test script guidance
test-hdmi-cec.sh: respect ENV=development (skip option 5), explicit .env load, ASCII output, 30s wait
display_manager: remove emoji from logs to avoid Unicode errors

HDMI_CEC_DEV_MODE.md

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+# HDMI-CEC Development Mode Behavior
+
+## Overview
+HDMI-CEC TV control is **automatically disabled** in development mode to prevent constantly switching the TV on/off during testing and development work.
+
+## How It Works
+
+### Automatic Behavior
+```python
+# In display_manager.py
+if ENV == "development":
+    CEC_ENABLED = False  # Override user setting
+```
+
+### Configuration Priority
+1. **Development Mode** (`ENV=development`): CEC always **OFF** (regardless of `CEC_ENABLED` setting)
+2. **Production Mode** (`ENV=production`): CEC respects `CEC_ENABLED` setting
+
+### Log Messages
+- **Development**: `🔧 Development mode: HDMI-CEC automatically disabled (TV control off)`
+- **Production + Enabled**: `📺 HDMI-CEC enabled: TV control active (device: 0)`
+- **Production + Disabled**: `📺 HDMI-CEC disabled in configuration`
+
+## Why Local Configuration?
+
+This is **local configuration** (not server-controlled) because:
+
+### ✅ Best Practice Reasons
+1. **Hardware-specific** - TV control is a local hardware concern
+2. **Independent operation** - Works without server connection
+3. **Developer workflow** - Fast toggle without server changes
+4. **Existing pattern** - Follows established `ENV` variable pattern
+5. **No deployment needed** - Change `.env` and restart
+
+### ❌ Why NOT Server-Controlled?
+1. Would require server deployment for local dev changes
+2. Adds network dependency to hardware feature
+3. Complicates client logic (need to fetch setting)
+4. Server shouldn't control local hardware behavior
+5. Breaks offline/standalone operation
+
+## Usage
+
+### Development Workflow
+```bash
+# .env file
+ENV=development    # CEC automatically disabled
+CEC_ENABLED=true   # Ignored in dev mode
+
+# Start Display Manager
+./scripts/start-display-manager.sh
+# Output: 🔧 Development mode: HDMI-CEC automatically disabled
+```
+
+### Production Deployment
+```bash
+# .env file
+ENV=production     # CEC respects setting
+CEC_ENABLED=true   # TV control active
+
+# Start Display Manager
+./scripts/start-display-manager.sh
+# Output: 📺 HDMI-CEC enabled: TV control active (device: 0)
+```
+
+### Force Enable CEC in Development (for testing)
+If you need to test CEC functionality during development:
+
+**Option 1: Temporarily set production mode**
+```bash
+# In .env
+ENV=production     # Enables CEC
+CEC_ENABLED=true
+```
+
+**Option 2: Use test scripts**
+```bash
+# Test CEC without starting Display Manager
+./scripts/test-hdmi-cec.sh         # Interactive menu
+./scripts/test-tv-response.sh      # Diagnostic test
+```
+
+## Configuration Reference
+
+### .env File
+```bash
+# Environment mode
+ENV=development    # or 'production'
+
+# HDMI-CEC TV Control
+# NOTE: Automatically DISABLED when ENV=development
+CEC_ENABLED=true
+CEC_DEVICE=0
+CEC_TURN_OFF_DELAY=30
+CEC_POWER_ON_WAIT=5
+CEC_POWER_OFF_WAIT=5
+```
+
+## Testing CEC Functionality
+
+### Without Starting Display Manager
+```bash
+# Interactive testing menu
+./scripts/test-hdmi-cec.sh
+
+# Diagnostic test with detailed feedback
+./scripts/test-tv-response.sh
+
+# Manual commands
+echo "on 0" | cec-client -s -d 1      # Turn TV on
+echo "standby 0" | cec-client -s -d 1 # Turn TV off
+echo "pow 0" | cec-client -s -d 1     # Check status
+```
+
+### With Display Manager
+```bash
+# Temporarily enable production mode
+ENV=production ./scripts/start-display-manager.sh
+
+# Or edit .env first
+vim .env  # Set ENV=production
+./scripts/start-display-manager.sh
+```
+
+## Architecture Decision
+
+### Chosen: Local Configuration
+- ✅ Simple and maintainable
+- ✅ Fast development workflow
+- ✅ No server dependency
+- ✅ Follows project patterns
+
+### Rejected: Server-Controlled
+- ❌ Adds complexity
+- ❌ Requires network/server
+- ❌ Slower iteration
+- ❌ Wrong abstraction level
+
+### Comparison
+
+| Aspect | Local Config | Server Config |
+|--------|-------------|---------------|
+| Toggle speed | Instant (restart) | Requires server deployment |
+| Network dependency | None | Required |
+| Offline operation | ✅ Works | ❌ Breaks |
+| Development workflow | ✅ Simple | ❌ Complex |
+| Hardware abstraction | ✅ Correct | ❌ Wrong level |
+| Server concern | ❌ No | ✅ Yes |
+
+## Related Files
+
+- **Implementation**: `src/display_manager.py` (lines 48-76)
+- **Configuration**: `.env` (CEC section)
+- **Testing**: `scripts/test-hdmi-cec.sh`, `scripts/test-tv-response.sh`
+- **Documentation**: `HDMI_CEC_SETUP.md`, `HDMI_CEC_IMPLEMENTATION.md`
+
+## Summary
+
+🎯 **HDMI-CEC is automatically disabled in development mode** to prevent TV switching during testing.
+
+🔧 **To test CEC**: Use test scripts or temporarily set `ENV=production`
+
+📺 **In production**: CEC respects `CEC_ENABLED` setting and works as expected
+
+🏗️ **Architecture**: Local configuration is best practice for hardware-specific behavior