fix: expand SQLite home and environment paths

src/main.rs

@@ -20,6 +20,8 @@ Use the in-app password field to keep credentials out of process arguments.
 Open an existing SQLite database file (read-only; missing files are not created):
   cargo run -- --sqlite ./database.sqlite
 SQLite paths can be relative or absolute; quote paths containing spaces.
+SQLite paths expand leading ~, $VAR, and ${VAR}; undefined variables are errors.
+Expansion never runs shell commands. Quote CLI paths to let dbdash expand them.
 
 PostgreSQL URLs and libpq-style key=value strings are accepted.
 Use sslmode=require for mandatory TLS; certificates and hostnames are verified.