feat(cli): add --model option to run command for model override

Add -m, --model <provider/model> option to oh-my-opencode run command.
Allows users to override the model while keeping the agent unchanged.

Changes:
- Add model?: string to RunOptions interface
- Create model-resolver.ts to parse provider/model format
- Add model-resolver.test.ts with 7 test cases (TDD)
- Add --model CLI option with help text examples
- Wire resolveRunModel in runner.ts and pass to promptAsync
- Export resolveRunModel from barrel (index.ts)

Example usage:
  bunx oh-my-opencode run --model anthropic/claude-sonnet-4 "Fix the bug"
  bunx oh-my-opencode run --agent Sisyphus --model openai/gpt-5.4 "Task"

src/cli/run/runner.ts

@@ -7,6 +7,7 @@ import { resolveSession } from "./session-resolver"
 import { createJsonOutputManager } from "./json-output"
 import { executeOnCompleteHook } from "./on-complete-hook"
 import { resolveRunAgent } from "./agent-resolver"
+import { resolveRunModel } from "./model-resolver"
 import { pollForCompletion } from "./poll-for-completion"
 import { loadAgentProfileColors } from "./agent-profile-colors"
 import { suppressRunInput } from "./stdin-suppression"
@@ -46,6 +47,7 @@ export async function run(options: RunOptions): Promise<number> {
 
   const pluginConfig = loadPluginConfig(directory, { command: "run" })
   const resolvedAgent = resolveRunAgent(options, pluginConfig)
+  const resolvedModel = resolveRunModel(options.model)
   const abortController = new AbortController()
 
   try {
@@ -78,6 +80,10 @@ export async function run(options: RunOptions): Promise<number> {
 
       console.log(pc.dim(`Session: ${sessionID}`))
 
+      if (resolvedModel) {
+        console.log(pc.dim(`Model: ${resolvedModel.providerID}/${resolvedModel.modelID}`))
+      }
+
       const ctx: RunContext = {
         client,
         sessionID,
@@ -96,6 +102,7 @@ export async function run(options: RunOptions): Promise<number> {
         path: { id: sessionID },
         body: {
           agent: resolvedAgent,
+          ...(resolvedModel ? { model: resolvedModel } : {}),
           tools: {
             question: false,
           },