fix: centralize model prefix handling to prevent provider errors

Moves prefix stripping from individual providers to AgentService/IdeationService
and adds validation to ensure providers receive bare model IDs. This prevents
bugs like the Codex CLI receiving "codex-gpt-5.1-codex-max" instead of the
expected "gpt-5.1-codex-max".

- Add validateBareModelId() helper with fail-fast validation
- Add originalModel field to ExecuteOptions for logging
- Update all providers to validate model has no prefix
- Centralize prefix stripping in service layer
- Remove redundant prefix stripping from individual providers

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

apps/server/src/providers/claude-provider.ts

@@ -10,7 +10,7 @@ import { BaseProvider } from './base-provider.js';
 import { classifyError, getUserFriendlyErrorMessage, createLogger } from '@automaker/utils';
 
 const logger = createLogger('ClaudeProvider');
-import { getThinkingTokenBudget } from '@automaker/types';
+import { getThinkingTokenBudget, validateBareModelId } from '@automaker/types';
 import type {
   ExecuteOptions,
   ProviderMessage,
@@ -53,6 +53,10 @@ export class ClaudeProvider extends BaseProvider {
    * Execute a query using Claude Agent SDK
    */
   async *executeQuery(options: ExecuteOptions): AsyncGenerator<ProviderMessage> {
+    // Validate that model doesn't have a provider prefix
+    // AgentService should strip prefixes before passing to providers
+    validateBareModelId(options.model, 'ClaudeProvider');
+
     const {
       prompt,
       model,