feat: add fts indexing

db/schema.sql

@@ -32,3 +32,11 @@ CREATE INDEX idx_symbols_exported ON symbols(exported, kind);
 CREATE INDEX idx_files_path ON files(path);
 CREATE INDEX idx_files_language ON files(language);
 CREATE INDEX idx_files_package ON files(package);
+
+-- FTS5 virtual table for full-text search of file contents.
+-- content is stored here (not external content), keyed by file_id.
+CREATE VIRTUAL TABLE file_contents USING fts5(
+    file_id UNINDEXED,
+    content,
+    tokenize='porter unicode61'
+);