fix(#2852): forward model overrides from categories/agent config to subagents

- fix(switcher): use lastIndexOf for multi-slash model IDs (e.g. aws/anthropic/claude-sonnet-4)
- fix(model-resolution): same lastIndexOf fix in doctor parseProviderModel
- fix(call-omo-agent): resolve model from agent config and forward to both
  background and sync executors via DelegatedModelConfig
- fix(subagent-resolver): inherit category model/variant when agent uses
  category reference without explicit model override
- test: add model override forwarding tests for call-omo-agent
- test: add multi-slash model ID test for switcher

src/cli/doctor/checks/model-resolution.ts

@@ -9,7 +9,7 @@ import { buildEffectiveResolution, getEffectiveModel } from "./model-resolution-
 import type { AgentResolutionInfo, CategoryResolutionInfo, ModelResolutionInfo, OmoConfig } from "./model-resolution-types"
 
 function parseProviderModel(value: string): { providerID: string; modelID: string } | null {
-  const slashIndex = value.indexOf("/")
+  const slashIndex = value.lastIndexOf("/")
   if (slashIndex <= 0 || slashIndex === value.length - 1) {
     return null
   }