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

tests/lang_stats_test.rs

@@ -0,0 +1,150 @@
+mod common;
+
+use gitks::pb::GetLanguageStatsRequest;
+use gitks::repository::lang_stats::{EXTENSION_MAP, FILENAME_MAP};
+
+#[test]
+fn test_extension_map_lookup() {
+    // Verify .md is in the map
+    let result = EXTENSION_MAP.binary_search_by(|&(e, _, _)| e.cmp(".md"));
+    assert!(result.is_ok(), ".md should be in EXTENSION_MAP, got {:?}", result);
+    let idx = result.unwrap();
+    assert_eq!(EXTENSION_MAP[idx].1, "Markdown");
+    assert_eq!(EXTENSION_MAP[idx].2, "prose");
+
+    // Verify .rs is in the map
+    let result = EXTENSION_MAP.binary_search_by(|&(e, _, _)| e.cmp(".rs"));
+    assert!(result.is_ok(), ".rs should be in EXTENSION_MAP");
+    let idx = result.unwrap();
+    assert_eq!(EXTENSION_MAP[idx].1, "Rust");
+}
+
+#[test]
+fn test_filename_map_lookup() {
+    // Verify Makefile is in the map
+    let result = FILENAME_MAP.binary_search_by(|&(f, _, _)| f.cmp("Makefile"));
+    assert!(result.is_ok(), "Makefile should be in FILENAME_MAP");
+}
+
+#[test]
+fn test_language_stats_basic() {
+    let (_dir, gb) = common::setup_bare_repo();
+
+    let resp = gb
+        .get_language_stats(GetLanguageStatsRequest {
+            repository: None,
+            revision: None,
+            path: String::new(),
+            max_file_size: 0,
+        })
+        .expect("get_language_stats");
+
+    // Should have some files
+    assert!(resp.total_files > 0, "expected some files");
+    assert!(resp.total_bytes > 0, "expected some bytes");
+
+    // Should detect Markdown (README.md)
+    let md = resp.languages.iter().find(|l| l.language == "Markdown");
+    assert!(md.is_some(), "should detect Markdown language");
+    let md = md.unwrap();
+    assert!(md.file_count > 0);
+    assert!(md.bytes > 0);
+    assert!(md.lines > 0);
+
+    // Should detect Rust (src/lib/mod.rs)
+    let rust = resp.languages.iter().find(|l| l.language == "Rust");
+    assert!(rust.is_some(), "should detect Rust language");
+    let rust = rust.unwrap();
+    assert!(rust.file_count > 0);
+
+    // Percentages should sum to ~100%
+    let total_pct: f64 = resp.languages.iter().map(|l| l.percentage).sum();
+    assert!(
+        (total_pct - 100.0).abs() < 0.01,
+        "percentages should sum to 100, got {total_pct}"
+    );
+
+    // Languages should be sorted by bytes descending
+    for i in 1..resp.languages.len() {
+        assert!(
+            resp.languages[i - 1].bytes >= resp.languages[i].bytes,
+            "languages should be sorted by bytes descending"
+        );
+    }
+}
+
+#[test]
+fn test_language_stats_lang_type() {
+    let (_dir, gb) = common::setup_bare_repo();
+
+    let resp = gb
+        .get_language_stats(GetLanguageStatsRequest {
+            repository: None,
+            revision: None,
+            path: String::new(),
+            max_file_size: 0,
+        })
+        .expect("get_language_stats");
+
+    // Markdown should be "prose" type
+    let md = resp.languages.iter().find(|l| l.language == "Markdown");
+    if let Some(md) = md {
+        assert_eq!(md.lang_type, "prose", "Markdown should be prose type");
+    }
+
+    // Rust should be "programming" type
+    let rust = resp.languages.iter().find(|l| l.language == "Rust");
+    if let Some(rust) = rust {
+        assert_eq!(
+            rust.lang_type, "programming",
+            "Rust should be programming type"
+        );
+    }
+}
+
+#[test]
+fn test_language_stats_with_path() {
+    let (_dir, gb) = common::setup_bare_repo();
+
+    // Restrict to "src" subdirectory
+    let resp = gb
+        .get_language_stats(GetLanguageStatsRequest {
+            repository: None,
+            revision: None,
+            path: "src".to_string(),
+            max_file_size: 0,
+        })
+        .expect("get_language_stats");
+
+    // Should find Rust files in src/
+    let rust = resp.languages.iter().find(|l| l.language == "Rust");
+    assert!(rust.is_some(), "should find Rust in src/ directory");
+
+    // Should NOT find README.md (it's at root level)
+    let md = resp.languages.iter().find(|l| l.language == "Markdown");
+    assert!(
+        md.is_none(),
+        "should not find Markdown in src/ directory"
+    );
+}
+
+#[test]
+fn test_language_stats_line_count_excludes_blank_lines() {
+    let (_dir, gb) = common::setup_bare_repo();
+
+    let resp = gb
+        .get_language_stats(GetLanguageStatsRequest {
+            repository: None,
+            revision: None,
+            path: String::new(),
+            max_file_size: 0,
+        })
+        .expect("get_language_stats");
+
+    // README.md has "# Test\n\nUpdated.\n" = 3 lines but only 2 non-blank lines
+    let md = resp.languages.iter().find(|l| l.language == "Markdown");
+    if let Some(md) = md {
+        // README.md: "# Test" and "Updated." are non-blank = 2 lines
+        assert!(md.lines >= 2, "should count at least 2 code lines for README.md");
+    }
+}