Polaris <Select> in this App Bridge + Polaris version is fully controlled —
without value+onChange it renders but ignores the user's choice (same class
of bug as commit cc20f20 for <TextField>). The "Add slot template",
"Add blackout date" and "Add rate" forms each had one or more inert
dropdowns, so nothing could be selected. Wired each to local state.
Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>