feat(cli): add doctor check for model resolution

Add new 'model-resolution' check to diagnose model fallback chain health. Validates that configured agents and categories can resolve to available models, surfacing misconfiguration early.

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/oh-my-opencode)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

src/cli/doctor/constants.ts

@@ -21,6 +21,7 @@ export const CHECK_IDS = {
   OPENCODE_INSTALLATION: "opencode-installation",
   PLUGIN_REGISTRATION: "plugin-registration",
   CONFIG_VALIDATION: "config-validation",
+  MODEL_RESOLUTION: "model-resolution",
   AUTH_ANTHROPIC: "auth-anthropic",
   AUTH_OPENAI: "auth-openai",
   AUTH_GOOGLE: "auth-google",
@@ -38,6 +39,7 @@ export const CHECK_NAMES: Record<string, string> = {
   [CHECK_IDS.OPENCODE_INSTALLATION]: "OpenCode Installation",
   [CHECK_IDS.PLUGIN_REGISTRATION]: "Plugin Registration",
   [CHECK_IDS.CONFIG_VALIDATION]: "Configuration Validity",
+  [CHECK_IDS.MODEL_RESOLUTION]: "Model Resolution",
   [CHECK_IDS.AUTH_ANTHROPIC]: "Anthropic (Claude) Auth",
   [CHECK_IDS.AUTH_OPENAI]: "OpenAI (ChatGPT) Auth",
   [CHECK_IDS.AUTH_GOOGLE]: "Google (Gemini) Auth",