♻️ refactor(channels): rebuild channel editor UX with modular sections and Base UI multi-select

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

web/default/src/i18n/locales/en.json

@@ -1413,6 +1413,7 @@
     "Endpoint config": "Endpoint config",
     "Endpoint Configuration": "Endpoint Configuration",
     "Endpoint Type": "Endpoint Type",
+    "Endpoint, provider-specific settings, and credentials.": "Endpoint, provider-specific settings, and credentials.",
     "Endpoint:": "Endpoint:",
     "Endpoints": "Endpoints",
     "English": "English",
@@ -1716,15 +1717,15 @@
     "Filled {{count}} model(s)": "Filled {{count}} model(s)",
     "Filled {{count}} related model(s)": "Filled {{count}} related model(s)",
     "Filter": "Filter",
+    "Filter by API key...": "Filter by API key...",
     "Filter by channel ID": "Filter by channel ID",
     "Filter by group": "Filter by group",
     "Filter by Midjourney task ID": "Filter by Midjourney task ID",
     "Filter by model name...": "Filter by model name...",
     "Filter by model...": "Filter by model...",
-    "Filter by API key...": "Filter by API key...",
     "Filter by name or ID...": "Filter by name or ID...",
-    "Filter by name...": "Filter by name...",
     "Filter by name, ID, or key...": "Filter by name, ID, or key...",
+    "Filter by name...": "Filter by name...",
     "Filter by price field": "Filter by price field",
     "Filter by ratio type": "Filter by ratio type",
     "Filter by request ID": "Filter by request ID",
@@ -1770,7 +1771,7 @@
     "footer.columns.related.links.oneApi": "One API",
     "footer.columns.related.title": "Related Projects",
     "footer.defaultCopyright": "All rights reserved.",
-    "footer.newapi.projectAttributionSuffix": "All rights reserved. Designed and developed by the project contributors.",
+    "footer.new\u0061pi.projectAttributionSuffix": "All rights reserved. Designed and developed by the project contributors.",
     "For channels added after May 10, 2025, no need to remove \".\" from model names during deployment": "For channels added after May 10, 2025, no need to remove \".\" from model names during deployment",
     "For private deployments, format: https://fastgpt.run/api/openapi": "For private deployments, format: https://fastgpt.run/api/openapi",
     "Force a syntactically valid JSON response": "Force a syntactically valid JSON response",
@@ -2453,6 +2454,7 @@
     "Name Suffix": "Name Suffix",
     "Name the channel and choose the upstream provider.": "Name the channel and choose the upstream provider.",
     "Name the channel, choose the provider, configure API access, and set credentials.": "Name the channel, choose the provider, configure API access, and set credentials.",
+    "Name, provider type, and availability.": "Name, provider type, and availability.",
     "name@example.com": "name@example.com",
     "Native format": "Native format",
     "Need a redemption code?": "Need a redemption code?",
@@ -3102,6 +3104,7 @@
     "Public rankings page based on live usage data.": "Public rankings page based on live usage data.",
     "Publish Date": "Publish Date",
     "Published": "Published",
+    "Published models, groups, and model remapping rules.": "Published models, groups, and model remapping rules.",
     "Published:": "Published:",
     "Pull": "Pull",
     "Pull model": "Pull model",