fix(web): repair Environment select in Freeze dialog

Context

The page-level Freeze an environment dialog has a broken Environment dropdown/suggestion UI.

From the reported screenshot, opening the Environment control renders a menu that is visually off-token and misaligned inside the dialog:

• popup background/color does not match the dialog/select theme
• menu width/position is awkward relative to the trigger
• popup overlaps the helper text/next field area in a rough way
• it looks like the select/datalist/shadcn configuration is incomplete

This is especially visible in dark theme.

Important Product Constraint

The page-level freeze flow must continue to allow free-text environment names.

Environments are created lazily after the first deploy, so freezing pre-emptively must support names that are not in the existing environment list yet. Existing environments should be suggestions, not a hard constraint, unless we intentionally design a combobox/custom-value flow.

Likely Area

• web/components/environments/freeze-dialog.client.tsx
• web/components/environments/freeze-dialog.test.tsx
• possibly web/components/ui/select.tsx if this is a shared shadcn/base-ui Select configuration issue

The component currently has prior context around avoiding Select inside Dialog because of a base-ui stack crash. If we switch to shadcn/base-ui Select or Combobox here, verify that the dialog/popover interaction is safe.

Acceptance Criteria

• Environment suggestions in the Freeze dialog render with correct app tokens in dark and light themes.
• Popup is aligned to the trigger, has sane width, and appears above the dialog content without visual clipping or odd overlap.
• Keyboard behavior works: focus, arrow navigation, Enter/select, Escape/close, Tab order.
• Free-text submission still works for an environment name that is not in the suggestion list.
• Per-card freeze mode remains unchanged: fixed environment, no editable Environment control.
• No extra backend fetch is added on type/open; reuse environments already available to the page where possible.
• Add/update tests covering:
  • suggestions render/open in the page-level Freeze dialog
  • selecting an existing environment works
  • typing and submitting a new environment name still works
  • dialog remains mounted/usable after the suggestion popup closes

Notes

Reported from Screenshot_20260809_121026.png: the Environment dropdown in the Freeze modal appears visually broken.

Start in web/components/environments/freeze-dialog.client.tsx and read web/components/environments/freeze-dialog.test.tsx; reproduce the page-level Freeze dialog behavior in both themes and review web/components/ui/select.tsx if the shared configuration is involved. Done means aligned, keyboard-usable suggestions, working existing and free-text environment submission, unchanged per-card mode, and tests covering popup closing and dialog usability.