phsl / new-api

Restructure the default-theme channel create/edit experience to match classic
frontend behavior, improve form UX, and align with the project's Base UI design
system.

Channel editor architecture:
- Split the monolithic channel mutate drawer into focused section components
  (basic, API access, auth, models, advanced) with shared drawer layout
  primitives
- Extract submission, toast handling, and react-query cache invalidation into
  `useChannelMutateForm`
- Add a dedicated loading skeleton for channel detail fetch during edit mode
- Remove the top-level configuration summary block

Form validation and data handling:
- Strengthen `channel-form` Zod schema with JSON, model mapping, status code
  mapping, Codex credential, and Vertex AI key refinements
- Move type-specific conditional validation into `superRefine`
- Normalize base URL formatting and tighten model mapping value validation

Model mapping editor:
- Add Visual/JSON tabbed editing with inline JSON and duplicate-key feedback
- Improve accessibility for icon-only actions and add model suggestion datalists

MultiSelect component:
- Replace the custom cmdk-based implementation with Base UI Combobox chips
- Align focus, border, ring, disabled, and invalid states with standard Input
  styling via `ComboboxChips`
- Preserve existing API for all current callers (`options`, `selected`,
  `onChange`, `allowCreate`, `createLabel`)
- Support inline custom value creation and comma/newline batch input
- Limit visible chips with a compact "+N more" overflow summary via
  `maxVisibleChips` (8 in the channel editor)
- Anchor the dropdown to the full chips container via `useComboboxAnchor` so
  the popup matches input width and long model names are no longer truncated

Models & groups UX:
- Integrate manual custom model entry directly into the model MultiSelect
- Remove the separate manual model input/button block
- Keep selected-model count badge and existing model-mapping guardrail behavior

i18n:
- Add and sync translation keys for section descriptions, validation messages,
  model mapping UI, and MultiSelect labels across en, zh, fr, ja, ru, and vi
- Fix missing translations for "Name, provider type, and availability.",
  "Endpoint, provider-specific settings, and credentials.", and "Published
  models, groups, and model remapping rules."
- Remove obsolete keys tied to the deprecated summary and manual model entry UI