refactor(providers): move oauth/ to providers/oauth/ and simplify model names

- Move src/agent/oauth/ to src/agent/providers/oauth/ (parent-child structure)
- Delete deprecated oauth/providers.ts re-export file
- Simplify Claude model names: claude-opus-4-5 (without date suffix)
- Update Codex models to current lineup (gpt-5.2, gpt-5.1-codex, etc.)
- Set claude-opus-4-5 as default model for claude-code provider

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/agent/oauth/index.ts

@@ -1,2 +0,0 @@
-export * from "./cli-credentials.js";
-export * from "./providers.js";

src/agent/oauth/providers.ts

@@ -1,20 +0,0 @@
-/**
- * @deprecated This file is deprecated. Import from '../providers/index.js' instead.
- *
- * This file re-exports from the new providers/ module for backwards compatibility.
- * Will be removed in a future version.
- */
-
-export {
-  type AuthMethod,
-  type ProviderInfo,
-  type ProviderConfig,
-  isOAuthProvider,
-  isProviderAvailable,
-  getCurrentProvider,
-  getProviderList,
-  getAvailableProviders,
-  formatProviderStatus,
-  getLoginInstructions,
-  resolveProviderConfig,
-} from "../providers/index.js";

src/agent/providers/oauth/index.ts

@@ -0,0 +1,7 @@
+/**
+ * OAuth Credential Reading
+ *
+ * Read OAuth credentials from external CLI tools (Claude Code, Codex).
+ */
+
+export * from "./cli-credentials.js";

src/agent/providers/registry.ts

@@ -9,7 +9,7 @@ import { credentialManager } from "../credentials.js";
 import {
   hasValidClaudeCliCredentials,
   hasValidCodexCliCredentials,
-} from "../oauth/cli-credentials.js";
+} from "./oauth/cli-credentials.js";
 
 // ============================================================
 // Types
@@ -50,24 +50,24 @@ const PROVIDER_REGISTRY: Record<string, ProviderMeta> = {
     id: "claude-code",
     name: "Claude Code (OAuth)",
     authMethod: "oauth",
-    defaultModel: "claude-sonnet-4-20250514",
-    models: ["claude-sonnet-4-20250514", "claude-opus-4-20250514"],
+    defaultModel: "claude-opus-4-5",
+    models: ["claude-opus-4-5", "claude-sonnet-4-5", "claude-haiku-4-5"],
     loginCommand: "claude login",
   },
   "openai-codex": {
     id: "openai-codex",
     name: "Codex (OAuth)",
     authMethod: "oauth",
-    defaultModel: "gpt-5.1",
-    models: ["gpt-5.1", "gpt-5.1-codex-max"],
+    defaultModel: "gpt-5.2",
+    models: ["gpt-5.2", "gpt-5.2-codex", "gpt-5.1-codex", "gpt-5.1-codex-mini", "gpt-5.1-codex-max"],
     loginCommand: "codex login",
   },
   "anthropic": {
     id: "anthropic",
     name: "Anthropic (API Key)",
     authMethod: "api-key",
-    defaultModel: "claude-sonnet-4-20250514",
-    models: ["claude-sonnet-4-20250514", "claude-opus-4-20250514", "claude-haiku-3-5-20241022"],
+    defaultModel: "claude-sonnet-4-5",
+    models: ["claude-opus-4-5", "claude-sonnet-4-5", "claude-haiku-4-5"],
     loginUrl: "https://console.anthropic.com/",
   },
   "openai": {

src/agent/providers/resolver.ts

@@ -10,7 +10,7 @@ import { credentialManager } from "../credentials.js";
 import {
   readClaudeCliCredentials,
   readCodexCliCredentials,
-} from "../oauth/cli-credentials.js";
+} from "./oauth/cli-credentials.js";
 import {
   PROVIDER_ALIAS,
   getProviderMeta,