fix: issue-triage quick wins (extraction, MCP probes, gitignore, CJK, impact) (#654)

Batch of small, localized fixes from an open-issue triage:

- .codegraph/.gitignore now ignores everything but itself, so the database,
  daemon.pid, sockets, and logs stop showing up in git status (#492, #484)
- MCP server answers resources/list and prompts/list with empty lists instead
  of -32601, clearing scary log lines in opencode/Codex (#621)
- index SAP HANA .xsjs/.xsjslib as JavaScript (#556) and TS .mts/.cts (#366)
- visit anonymous AMD/CommonJS/IIFE wrapper bodies so their inner functions and
  calls are indexed instead of coming up empty (#528)
- batch the changed-file lookup so a huge first sync no longer hits
  "too many SQL variables" (#540)
- list files with `git ls-files -z` so non-ASCII/CJK paths survive
  core.quotepath and are no longer silently skipped (#541)
- attach Go methods on generic receivers (*T[P]) to their type (#583, RC1)
- impact no longer climbs the structural `contains` edge, so a leaf symbol
  stops dragging in its sibling methods (#536)
- README: explicit `codegraph install` step, run in a new shell (#631)

Co-authored-by: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/extraction/grammars.ts

@@ -46,9 +46,15 @@ const WASM_GRAMMAR_FILES: Record<GrammarLanguage, string> = {
 export const EXTENSION_MAP: Record<string, Language> = {
   '.ts': 'typescript',
   '.tsx': 'tsx',
+  // ESM/CJS TypeScript module extensions — parsed as TS (no JSX). (#366)
+  '.mts': 'typescript',
+  '.cts': 'typescript',
   '.js': 'javascript',
   '.mjs': 'javascript',
   '.cjs': 'javascript',
+  // SAP HANA XS Classic server-side JavaScript. (#556)
+  '.xsjs': 'javascript',
+  '.xsjslib': 'javascript',
   '.jsx': 'jsx',
   '.py': 'python',
   '.pyw': 'python',