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.

src/resolution/import-resolver.ts

@@ -105,7 +105,7 @@ function resolveRelativeImport(
 
   // Try the path as-is first
   const basePath = path.resolve(fromDir, importPath);
-  const relativePath = path.relative(projectRoot, basePath);
+  const relativePath = path.relative(projectRoot, basePath).replace(/\\/g, '/');
 
   // Try each extension
   for (const ext of extensions) {