feat: implement bass control (GET/POST /bass)

- Add complete bass control functionality via GET/POST /bass endpoints
- Implement GetBass() for current bass level retrieval
- Add SetBass() with range validation (-9 to +9)
- Include IncreaseBass() and DecreaseBass() with safety limits
- Add SetBassSafe() with automatic value clamping
- Create comprehensive bass models with validation and helpers
- Add CLI flags: -bass, -set-bass, -inc-bass, -dec-bass
- Implement safety features with range validation and clamping
- Create comprehensive test suite (30+ test cases) with mock servers
- Add integration tests with real device validation (SoundTouch 10/20)
- Update documentation with complete BASS-CONTROLS.md guide
- Update API endpoints status (GET/POST /bass: ✅ Implemented)
- Update project status (55% overall completion, 80% control endpoints)
- Real device testing with bass adjustment and validation
- Error handling for invalid ranges and API responses
- XML request/response format validation and compliance
- Human-readable bass level descriptions and categorization

docs/API-Endpoints-Overview.md

@@ -126,7 +126,7 @@ Sets the volume.
 
 ## Bass Settings
 
-### GET /bass 🔄 **Planned**
+### GET /bass ✅ **Implemented**
 Retrieves the current bass settings.
 
 **Response XML:**
@@ -137,7 +137,7 @@ Retrieves the current bass settings.
 </bass>
 ```
 
-### POST /bass 🔄 **Planned**
+### POST /bass ✅ **Implemented**
 Sets the bass settings (-9 to +9).
 
 **Request XML:**