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.

tsconfig.json

@@ -24,7 +24,10 @@
     "esModuleInterop": true,
     "skipLibCheck": true,
     "forceConsistentCasingInFileNames": true,
-    "resolveJsonModule": true
+    "resolveJsonModule": true,
+    "paths": {
+      "web-tree-sitter": ["./src/web-tree-sitter.d.ts"]
+    }
   },
   "include": ["src/**/*"],
   "exclude": ["node_modules", "dist", "__tests__"]