feat: add ReScript language support

[malo]

Add ReScript (https://rescript-lang.org/) as a supported language with tree-sitter parsing for .res and .resi files.

The tree-sitter-rescript.wasm grammar (908KB) was built from https://github.com/rescript-lang/tree-sitter-rescript via Docker + emscripten. AST node mappings cover let_declaration, module_declaration, type_declaration, call_expression, pipe_expression, open_statement, and include_statement.

Fix symbol disambiguation in MCP tools: add file parameter to codegraph_node, codegraph_callers, codegraph_callees, and codegraph_impact so that ambiguous symbol names can be resolved by file path. When file is provided but no match is found, return an error instead of silently falling back to a different symbol.

[andreinknv]

Hi! Sorry to drop in cold — I've been working through the open PR backlog and noticed your PR is waiting on the same architectural conflict as a bunch of other language PRs. I've opened a refactor PR (#116) that turns "adding a language" from a 6-file mutation into a 1-file addition. Once that lands, this PR rebases cleanly. Sharing the rebase template inline so you don't have to read the maintainer guide to do it.

After #116 merges, the rebase is mechanical

Step 1. Discard your changes to the monolithic files (#116 makes them auto-derived from the registry):

git checkout main -- \
  src/types.ts \
  src/extraction/grammars.ts \
  src/extraction/languages/index.ts \
  CLAUDE.md

Step 2. Move your extractor's registration into one file, src/extraction/languages/<your-language>.ts:

import { yourExtractor } from './your-extractor-config';
import type { LanguageDef } from './types';

export const YOUR_DEF: LanguageDef = {
  name: 'yourlang',
  displayName: 'Your Language',
  extensions: ['.ext'],
  includeGlobs: ['**/*.ext'],
  // For a tree-sitter grammar:
  grammar: { wasmFile: 'tree-sitter-yourlang.wasm', vendored: true, extractor: yourExtractor },
  // OR for a custom regex/template extractor (Liquid, HCL pattern):
  // customExtractor: (filePath, source) => new YourExtractor(filePath, source).extract(),
};

Step 3. Add 2 lines to src/extraction/languages/registry.ts:

import { YOUR_DEF } from './yourlang';   // alphabetical
// ...
const ALL_DEFS: readonly LanguageDef[] = [
  // ... alphabetical
  YOUR_DEF,
  // ...
];

Step 4. Add 'yourlang' to the Language union in src/types.ts (1 line).

Step 5. Your test additions in __tests__/extraction.test.ts work as-is — the registry refactor doesn't touch tests.

That's it. If your existing <extractor>.ts file is in the right shape (taking filePath+source for custom extractors, or being a LanguageExtractor for grammar-backed), it requires zero changes — just register it via LanguageDef.

Three of my own language PRs (#92, #94, #95) are already pre-rebased to this pattern as references if you want to see what a finished rebase looks like.

Happy to help with the rebase if you'd like — just let me know.