feat(extraction): R language support (#828) (#839)

R has no declaration syntax — everything is an expression — so the
extractor works through the visitNode hook: functions in every
assignment form (incl. nested, attributed to their enclosing scope),
top-level variables/constants, library()/require() imports and
source() file references (claimed, Lua-style), S4/RefClass/R6/ggproto
classes with their methods and extends edges, setGeneric/setMethod.
Grammar vendored from r-lib/tree-sitter-r v1.2.0 (ABI 14; npm package
is a security placeholder, tree-sitter-wasms has no R).

Benchmarked on AnomalyDetection (8/8 named defs), dplyr (1027 fns),
ggplot2 (150 ggproto classes / 597 methods / 128 extends edges —
adding ggproto mid-bench flipped the large-repo A/B from a regression
to 2.4x faster than the no-codegraph arm).

Co-authored-by: Claude Opus 4.8 <noreply@anthropic.com>

src/extraction/grammars.ts

@@ -36,6 +36,7 @@ const WASM_GRAMMAR_FILES: Record<GrammarLanguage, string> = {
   pascal: 'tree-sitter-pascal.wasm',
   scala: 'tree-sitter-scala.wasm',
   lua: 'tree-sitter-lua.wasm',
+  r: 'tree-sitter-r.wasm',
   luau: 'tree-sitter-luau.wasm',
   objc: 'tree-sitter-objc.wasm',
 };
@@ -94,6 +95,7 @@ export const EXTENSION_MAP: Record<string, Language> = {
   '.svelte': 'svelte',
   '.vue': 'vue',
   '.astro': 'astro',
+  '.r': 'r',
   '.pas': 'pascal',
   '.dpr': 'pascal',
   '.dpk': 'pascal',
@@ -214,7 +216,7 @@ export async function loadGrammarsForLanguages(languages: Language[]): Promise<v
       // `class Foo(...)` as an ERROR that swallows the whole class (#237); we
       // vendor the upstream ABI-15 tree-sitter-c-sharp 0.23.5 wasm, which parses
       // primary constructors natively.
-      const wasmPath = (lang === 'pascal' || lang === 'scala' || lang === 'lua' || lang === 'luau' || lang === 'csharp')
+      const wasmPath = (lang === 'pascal' || lang === 'scala' || lang === 'lua' || lang === 'luau' || lang === 'csharp' || lang === 'r')
         ? path.join(__dirname, 'wasm', wasmFile)
         : require.resolve(`tree-sitter-wasms/out/${wasmFile}`);
       const language = await WasmLanguage.load(wasmPath);
@@ -401,6 +403,7 @@ export function getLanguageDisplayName(language: Language): string {
     python: 'Python',
     go: 'Go',
     rust: 'Rust',
+    r: 'R',
     java: 'Java',
     c: 'C',
     cpp: 'C++',