feat: unified Claude API key and profile system with z.AI, MiniMax, OpenRouter support (#600)

* feat: add Claude API provider profiles for alternative endpoints

Add support for managing multiple Claude-compatible API endpoints
(z.AI GLM, AWS Bedrock, etc.) through provider profiles in settings.

Features:
- New ClaudeApiProfile type with base URL, API key, model mappings
- Pre-configured z.AI GLM template with correct model names
- Profile selector in Settings > Claude > API Profiles
- Clean switching between profiles and direct Anthropic API
- Immediate persistence to prevent data loss on restart

Profile support added to all execution paths:
- Agent service (chat)
- Ideation service
- Auto-mode service (feature agents, enhancements)
- Simple query service (title generation, descriptions, etc.)
- Backlog planning, commit messages, spec generation
- GitHub issue validation, suggestions

Environment variables set when profile is active:
- ANTHROPIC_BASE_URL, ANTHROPIC_AUTH_TOKEN/API_KEY
- ANTHROPIC_DEFAULT_HAIKU/SONNET/OPUS_MODEL
- API_TIMEOUT_MS, CLAUDE_CODE_DISABLE_NONESSENTIAL_TRAFFIC

apps/server/src/routes/backlog-plan/generate-plan.ts

@@ -25,7 +25,11 @@ import {
   saveBacklogPlan,
 } from './common.js';
 import type { SettingsService } from '../../services/settings-service.js';
-import { getAutoLoadClaudeMdSetting, getPromptCustomization } from '../../lib/settings-helpers.js';
+import {
+  getAutoLoadClaudeMdSetting,
+  getPromptCustomization,
+  getActiveClaudeApiProfile,
+} from '../../lib/settings-helpers.js';
 
 const featureLoader = new FeatureLoader();
 
@@ -161,6 +165,13 @@ ${userPrompt}`;
       finalSystemPrompt = undefined; // System prompt is now embedded in the user prompt
     }
 
+    // Get active Claude API profile for alternative endpoint configuration
+    const { profile: claudeApiProfile, credentials } = await getActiveClaudeApiProfile(
+      settingsService,
+      '[BacklogPlan]',
+      projectPath
+    );
+
     // Execute the query
     const stream = provider.executeQuery({
       prompt: finalPrompt,
@@ -173,6 +184,8 @@ ${userPrompt}`;
       settingSources: autoLoadClaudeMd ? ['user', 'project'] : undefined,
       readOnly: true, // Plan generation only generates text, doesn't write files
       thinkingLevel, // Pass thinking level for extended thinking
+      claudeApiProfile, // Pass active Claude API profile for alternative endpoint configuration
+      credentials, // Pass credentials for resolving 'credentials' apiKeySource
     });
 
     let responseText = '';