Restore first-class OMO Slim council support (#1981) (#1982)

cc-switch could already persist arbitrary OMO Slim agent keys and top-level fields, but the built-in metadata and UI copy still reflected the pre-council agent set. This made the upstream council feature look unsupported and pushed users toward manual JSON-only setup.

Promote council to a built-in OMO Slim agent, add copy that points top-level plugin settings at Other Fields, and lock the behavior with regression tests.

Constraint: oh-my-opencode-slim exposes council through both agents.council and top-level council config
Rejected: Add a dedicated council editor UI now | too much surface area for issue #1981
Confidence: high
Scope-risk: narrow
Reversibility: clean
Directive: Keep OMO Slim built-in agent metadata aligned with upstream agent additions before shipping UI support
Tested: pnpm exec vitest run tests/utils/omoConfig.test.ts tests/components/OmoFormFields.mergeCustomModelsIntoStore.test.ts
Tested: pnpm typecheck
Not-tested: End-to-end validation against a live oh-my-opencode-slim installation
Related: farion1231/cc-switch#1981

src/types/omo.ts

@@ -362,6 +362,14 @@ export const OMO_SLIM_BUILTIN_AGENTS: OmoAgentDef[] = [
     recommended: "gpt-5.4",
     group: "sub",
   },
+  {
+    key: "council",
+    display: "Council",
+    descKey: "omo.slimAgentDesc.council",
+    tooltipKey: "omo.slimAgentTooltip.council",
+    recommended: "gpt-5.4-mini",
+    group: "sub",
+  },
 ];
 
 export const OMO_SLIM_DISABLEABLE_AGENTS = [
@@ -371,6 +379,7 @@ export const OMO_SLIM_DISABLEABLE_AGENTS = [
   { value: "explorer", label: "Explorer" },
   { value: "designer", label: "Designer" },
   { value: "fixer", label: "Fixer" },
+  { value: "council", label: "Council" },
 ] as const;
 
 export const OMO_SLIM_DISABLEABLE_MCPS = [