Marketplace gh login: tear down the container login on every failure

A lost stream or a failed Enter write returned without killing the
in-container gh, leaving it polling with a temp GH_CONFIG_DIR that would
receive the token. The output loop is now drive_login (generic over the
stream, writer and emitter, so it is unit-tested without Docker), and
its result goes through cleanup_on_error, so every ending except a token
read back runs the pkill. Neutral wording for the shared ANSI stripper's
overflow warning.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

app/src-tauri/src/commands/auth_token_commands.rs

@@ -644,7 +644,7 @@ impl AnsiStripper {
         // fresh chunk, which re-enters here.
         if self.carry.len() > MAX_ANSI_CARRY {
             log::warn!(
-                "`claude setup-token` emitted an unterminated control sequence \
+                "the command emitted an unterminated control sequence \
                  longer than {} bytes — treating it as text",
                 MAX_ANSI_CARRY
             );