refactor: remove AX_DB_PATH env var, fix Dockerfile for src/ layout

src/store/graph_store_sqlite.go

@@ -59,14 +59,9 @@ func InitSQLiteStore(path string) error {
 	return nil
 }
 
-// FindAndOpenSQLiteStore opens the SQLite database. If the AX_DB_PATH environment
-// variable is set, it uses that path directly. Otherwise, it walks up from the
+// FindAndOpenSQLiteStore opens the SQLite database by walking up from the
 // current working directory to find an .ax/ax.db file.
 func FindAndOpenSQLiteStore() (GraphStore, error) {
-	if dbpath := os.Getenv("AX_DB_PATH"); dbpath != "" {
-		return NewSQLiteStore(dbpath)
-	}
-
 	dataRoot, err := FindDataRoot(".local", "share")
 	if err != nil {
 		return nil, fmt.Errorf("failed to find data dir: %w", err)