Add WASM fallbacks for tree-sitter and SQLite, fix installer

Replace native tree-sitter with web-tree-sitter + tree-sitter-wasms for
universal cross-platform support. Add node-sqlite3-wasm as a fallback
when better-sqlite3 native bindings aren't available. Move better-sqlite3
and sqlite-vss to optionalDependencies so installs never fail.

Fix installer to use npx fallback when global npm install fails, so MCP
config, hooks, and quick-start instructions all work without the bare
codegraph command in PATH.

Fix tests: update schema version expectation, fix db test paths and
method names, extract MAX_OUTPUT_LENGTH as module constant, normalize
Windows path separators in import resolver.

__tests__/extraction.test.ts

@@ -4,16 +4,20 @@
  * Tests for the tree-sitter extraction system.
  */
 
-import { describe, it, expect, beforeEach, afterEach } from 'vitest';
+import { describe, it, expect, beforeAll, beforeEach, afterEach } from 'vitest';
 import * as fs from 'fs';
 import * as path from 'path';
 import * as os from 'os';
 import { CodeGraph } from '../src';
 import { extractFromSource, scanDirectory, shouldIncludeFile } from '../src/extraction';
-import { detectLanguage, isLanguageSupported, getSupportedLanguages } from '../src/extraction/grammars';
+import { detectLanguage, isLanguageSupported, getSupportedLanguages, initGrammars } from '../src/extraction/grammars';
 import { normalizePath } from '../src/utils';
 import { DEFAULT_CONFIG } from '../src/types';
 
+beforeAll(async () => {
+  await initGrammars();
+});
+
 // Create a temporary directory for each test
 function createTempDir(): string {
   return fs.mkdtempSync(path.join(os.tmpdir(), 'codegraph-test-'));