feat(repository): add language statistics analysis feature

- Remove data directory from gitignore to include language data
- Add build script to parse linguist languages.yml and generate static mappings
- Include serde and serde_yml dependencies for YAML parsing
- Add lang_stats module with language detection and statistics calculation
- Generate protobuf definitions for language statistics API endpoints
- Implement GetLanguageStats RPC endpoint in repository server
- Add comprehensive test suite for language statistics functionality
- Include extension and filename based language detection logic
- Implement binary file classification and group resolution features

proto/repository.proto

@@ -385,6 +385,30 @@ message GetRawChangesResponse {
 }
 
 
+message GetLanguageStatsRequest {
+  RepositoryHeader repository = 1;
+  ObjectSelector revision = 2;      // defaults to HEAD if unset
+  string path = 3;                  // optional: restrict to subdirectory
+  uint32 max_file_size = 4;         // skip files larger than this (bytes, 0 = 512KB default)
+}
+
+message GetLanguageStatsResponse {
+  repeated LanguageStat languages = 1;
+  uint64 total_files = 2;
+  uint64 total_bytes = 3;
+  uint64 total_lines = 4;
+}
+
+message LanguageStat {
+  string language = 1;              // language name, e.g. "Rust"
+  string lang_type = 2;             // "programming", "markup", "data", "prose"
+  uint64 file_count = 3;
+  uint64 bytes = 4;
+  uint64 lines = 5;
+  double percentage = 6;            // percentage by bytes
+}
+
+
 message FetchRemoteRequest {
   RepositoryHeader repository = 1;
   string remote_url = 2;
@@ -453,4 +477,5 @@ service RepositoryService {
   rpc FindLicense(FindLicenseRequest) returns (FindLicenseResponse);
   rpc OptimizeRepository(OptimizeRepositoryRequest) returns (OptimizeRepositoryResponse);
   rpc GetRawChanges(GetRawChangesRequest) returns (GetRawChangesResponse);
+  rpc GetLanguageStats(GetLanguageStatsRequest) returns (GetLanguageStatsResponse);
 }