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/vectors/manager.ts

@@ -4,7 +4,7 @@
  * High-level manager that coordinates embedding generation and vector search.
  */
 
-import Database from 'better-sqlite3';
+import { SqliteDatabase } from '../db/sqlite-adapter';
 import { Node, SearchResult, SearchOptions } from '../types';
 import { TextEmbedder, createEmbedder, EmbedderOptions, EMBEDDING_DIMENSION } from './embedder';
 import { VectorSearchManager, createVectorSearch } from './search';
@@ -68,7 +68,7 @@ export class VectorManager {
   private initialized = false;
 
   constructor(
-    db: Database.Database,
+    db: SqliteDatabase,
     queries: QueryBuilder,
     options: VectorManagerOptions = {}
   ) {
@@ -355,7 +355,7 @@ export class VectorManager {
  * Create a vector manager
  */
 export function createVectorManager(
-  db: Database.Database,
+  db: SqliteDatabase,
   queries: QueryBuilder,
   options?: VectorManagerOptions
 ): VectorManager {

src/vectors/search.ts

@@ -5,7 +5,7 @@
  * Falls back to brute-force cosine similarity if sqlite-vss is not available.
  */
 
-import Database from 'better-sqlite3';
+import { SqliteDatabase } from '../db/sqlite-adapter';
 import { Node } from '../types';
 import { TextEmbedder, EMBEDDING_DIMENSION } from './embedder';
 
@@ -29,11 +29,11 @@ export interface VectorSearchOptions {
  * Handles vector storage and similarity search for semantic code search.
  */
 export class VectorSearchManager {
-  private db: Database.Database;
+  private db: SqliteDatabase;
   private vssEnabled = false;
   private embeddingDimension: number;
 
-  constructor(db: Database.Database, dimension: number = EMBEDDING_DIMENSION) {
+  constructor(db: SqliteDatabase, dimension: number = EMBEDDING_DIMENSION) {
     this.db = db;
     this.embeddingDimension = dimension;
   }
@@ -75,10 +75,11 @@ export class VectorSearchManager {
       const vss = await import('sqlite-vss');
 
       // Use the load function which loads both vector0 and vss0
+      // VSS extension expects the raw better-sqlite3 Database instance
       if (typeof vss.load === 'function') {
-        vss.load(this.db);
+        vss.load(this.db as any);
       } else if (typeof vss.default?.load === 'function') {
-        vss.default.load(this.db);
+        vss.default.load(this.db as any);
       } else {
         throw new Error('sqlite-vss load function not found');
       }
@@ -464,7 +465,7 @@ export class VectorSearchManager {
  * Create a vector search manager
  */
 export function createVectorSearch(
-  db: Database.Database,
+  db: SqliteDatabase,
   dimension?: number
 ): VectorSearchManager {
   return new VectorSearchManager(db, dimension);