feat(admin-ui): load and edit router config from forms

Add a form-first LLM/TTS router config editor and a redacted admin config snapshot so operators can inspect configKV state before applying changes.

Preserve existing encrypted key entries when loaded slices are submitted without new plaintext keys.

Signed-off-by: RainbowBird <git@luoling.moe>
Commit-Message-Assisted-by: Claude (via Claude Code)

docs/ai/context/ui-components.md

@@ -448,6 +448,7 @@ All Field components wrap a base input with `label`, `description`, and consiste
 | `placeholder` | `string?` | — | Placeholder |
 | `required` | `boolean?` | — | Required indicator |
 | `type` | `InputType?` | — | Input type |
+| `autocomplete` | `string?` | — | Native autocomplete hint |
 | `inputClass` | `string?` | — | Custom input class |
 | `singleLine` | `boolean?` | `true` | `true` = input, `false` = textarea |