Implement sampling rate management with full CRUD operations

This commit introduces comprehensive sampling rate management functionality
to the MediaManager system, following the established patterns from BitDepth
and BitRate implementations.

Core Components Added:
- SamplingRate entity model with JPA annotations for database persistence
- SamplingRateRepository with full CRUD operations (save, findAll, findById, update, deleteById)
- SamplingRateService business logic layer with validation and error handling
- SamplingRateMapper for bidirectional entity-protobuf conversions

Protocol Buffers:
- Defined samplingrate.proto with complete message specifications
- SamplingRate message structure (id, value)
- Request/Response pairs for all CRUD operations (Create, GetAll, GetById, Update, Delete)
- Fixed typo in UpdateSamplingRateRequest (valeu -> value)

Action Handlers:
- CreateSamplingRateHandler: Validates and creates new sampling rate entries
- GetSamplingRateHandler: Retrieves all sampling rates from the database
- GetSamplingRateByIdHandler: Fetches individual sampling rates with 404 handling
- UpdateSamplingRateHandler: Updates existing sampling rates with validation
- DeleteSamplingRateHandler: Removes sampling rates with success confirmation

Integration:
- Registered SamplingRateService in DelegateActionManager
- All handlers follow the @Action annotation pattern for automatic discovery
- Consistent error handling with appropriate HTTP status codes (400, 404, 500)

This implementation provides a complete foundation for managing audio sampling
rates within the media management system, enabling clients to perform all
standard CRUD operations through the established protocol buffer interface.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

src/main/proto/samplingrate.proto

@@ -0,0 +1,51 @@
+syntax = "proto3";
+
+option java_package = "com.mediamanager.protocol.messages";
+option java_outer_classname = "SamplingRateMessages";
+
+package mediamanager.messages;
+
+message SamplingRate{
+  int32 id=1;
+  string value=2;
+}
+
+message CreateSamplingRateRequest{
+  string value= 1;
+}
+
+message CreateSamplingRateResponse{
+  SamplingRate samplingrate =1;
+}
+
+message GetSamplingRatesRequest{}
+
+message GetSamplingRatesResponse{
+  repeated SamplingRate samplingrates = 1;
+}
+
+message GetSamplingRateByIDRequest{
+  int32 id =1;
+}
+
+message GetSamplingRateByIdResponse{
+  SamplingRate samplingrate = 1;
+}
+
+message UpdateSamplingRateRequest{
+  int32 id = 1;
+  string value = 2;
+}
+
+message UpdateSamplingRateResponse{
+  SamplingRate samplingrate = 1;
+}
+
+message DeleteSamplingRateRequest{
+  int32 id =1;
+}
+
+message DeleteSamplingRateResponse{
+  bool success = 1;
+  string message =2;
+}