feat: add Codex CLI detection and model management APIs

- Implemented IPC handlers for checking Codex CLI installation status, retrieving available models, and checking provider statuses.
- Enhanced the SettingsView to include OpenAI API key management and connection testing.
- Updated the feature executor to support multiple model providers (Claude and Codex), allowing for improved flexibility in feature execution.
- Introduced utility functions to determine model types and support for thinking controls.

This update enhances the application's capabilities by integrating Codex CLI support and improving model management, providing users with a more robust experience.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

app/src/store/app-store.ts

@@ -32,6 +32,7 @@ export type KanbanCardDetailLevel = "minimal" | "standard" | "detailed";
 export interface ApiKeys {
   anthropic: string;
   google: string;
+  openai: string;
 }
 
 export interface ImageAttachment {
@@ -76,7 +77,22 @@ export interface FeatureImagePath {
 }
 
 // Available models for feature execution
-export type AgentModel = "opus" | "sonnet" | "haiku";
+// Claude models
+export type ClaudeModel = "opus" | "sonnet" | "haiku";
+// OpenAI/Codex models
+export type OpenAIModel =
+  | "gpt-5.1-codex-max"
+  | "gpt-5.1-codex"
+  | "gpt-5.1-codex-mini"
+  | "gpt-5.1"
+  | "o3"
+  | "o3-mini"
+  | "o4-mini";
+// Combined model type
+export type AgentModel = ClaudeModel | OpenAIModel;
+
+// Model provider type
+export type ModelProvider = "claude" | "codex";
 
 // Thinking level (budget_tokens) options
 export type ThinkingLevel = "none" | "low" | "medium" | "high" | "ultrathink";
@@ -226,6 +242,7 @@ const initialState: AppState = {
   apiKeys: {
     anthropic: "",
     google: "",
+    openai: "",
   },
   chatSessions: [],
   currentChatSession: null,