Port performance improvements from PR #15

- SQLite performance pragmas: synchronous=NORMAL, 64MB cache,
  memory temp store, 256MB mmap (safe with WAL mode)
- Batch insert for unresolved refs: single transaction instead of
  N individual inserts per file
- Symbol caching (warmCaches): pre-load all nodes into memory maps
  before resolution, eliminating repeated SQLite queries per ref
- Async file I/O: fs.stat/readFile in indexFile() are now non-blocking
- Denormalize filePath/language onto UnresolvedReference: avoids N
  node lookups during resolution, with schema migration v2

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/db/index.ts

@@ -41,6 +41,11 @@ export class DatabaseConnection {
     // Wait up to 2 minutes if database is locked by another process
     // (indexing operations can hold locks for extended periods)
     db.pragma('busy_timeout = 120000');
+    // Performance tuning
+    db.pragma('synchronous = NORMAL');     // Safe with WAL mode
+    db.pragma('cache_size = -64000');      // 64 MB page cache
+    db.pragma('temp_store = MEMORY');      // Temp tables in memory
+    db.pragma('mmap_size = 268435456');    // 256 MB memory-mapped I/O
 
     // Run schema initialization
     const schemaPath = path.join(__dirname, 'schema.sql');
@@ -66,6 +71,11 @@ export class DatabaseConnection {
     // Wait up to 2 minutes if database is locked by another process
     // (indexing operations can hold locks for extended periods)
     db.pragma('busy_timeout = 120000');
+    // Performance tuning
+    db.pragma('synchronous = NORMAL');
+    db.pragma('cache_size = -64000');
+    db.pragma('temp_store = MEMORY');
+    db.pragma('mmap_size = 268435456');
 
     // Check and run migrations if needed
     const conn = new DatabaseConnection(db, dbPath);