Implement bit-rate management feature

Add complete CRUD functionality for bit-rate management following the same pattern as bit-depth:
  - Create BitRate entity model with JPA annotations
  - Implement BitRateRepository with full CRUD operations
  - Add BitRateService with validation and business logic
  - Create BitRateMapper for protobuf/entity conversion
  - Implement action handlers: Create, GetAll, GetById, Update, Delete
  - Define bitrate.proto protobuf message definitions
  - Register BitRateService in DelegateActionManager

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

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

src/main/proto/bitrate.proto

@@ -0,0 +1,53 @@
+syntax = "proto3";
+
+option java_package = "com.mediamanager.protocol.messages";
+option java_outer_classname = "BitRateMessages";
+
+package mediamanager.messages;
+
+message BitRate{
+  int32 id =1;
+  string value = 2;
+}
+
+message CreateBitRateRequest{
+  string value = 1;
+}
+
+message CreateBitRateResponse{
+  BitRate bitrate = 1;
+}
+
+message GetBitRatesRequest{
+
+}
+
+message GetBitRatesResponse{
+  repeated BitRate bitrates = 1;
+}
+
+message GetBitRateByIdRequest{
+  int32 id = 1;
+}
+
+message GetBitRateByIdResponse{
+  BitRate bitrate = 1;
+}
+
+message UpdateBitRateRequest{
+  int32 id = 1;
+  string value = 2;
+}
+
+message UpdateBitRateResponse{
+  BitRate bitrate = 1;
+}
+
+message DeleteBitRateRequest{
+  int32 id =1;
+}
+
+message DeleteBitRateResponse{
+  bool success = 1;
+  string message = 2;
+}