feat: add GLM/alternative API support via environment variables

Add support for using alternative API endpoints (like Zhipu AI's GLM models)
without affecting the user's global Claude Code settings. Configuration is
done via AutoCoder's .env file.

Changes:
- Add API_ENV_VARS constant and pass through ClaudeAgentOptions.env parameter
  in client.py and all server service files (spec, expand, assistant sessions)
- Add glm_mode to settings API response to indicate when GLM is configured
- Add purple "GLM" badge in UI header when GLM mode is active
- Update setup status to accept GLM credentials as valid authentication
- Update .env.example with GLM configuration documentation
- Update README.md with AutoCoder-scoped GLM setup instructions

Supported environment variables:
- ANTHROPIC_BASE_URL: Custom API endpoint (e.g., https://api.z.ai/api/anthropic)
- ANTHROPIC_AUTH_TOKEN: API authentication token
- API_TIMEOUT_MS: Request timeout in milliseconds
- ANTHROPIC_DEFAULT_SONNET_MODEL: Model override for Sonnet
- ANTHROPIC_DEFAULT_OPUS_MODEL: Model override for Opus
- ANTHROPIC_DEFAULT_HAIKU_MODEL: Model override for Haiku

This approach routes API requests through the alternative endpoint while
keeping all Claude Code features (MCP servers, hooks, permissions) intact.

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

server/services/assistant_chat_session.py

@@ -33,6 +33,16 @@ logger = logging.getLogger(__name__)
 # Root directory of the project
 ROOT_DIR = Path(__file__).parent.parent.parent
 
+# Environment variables to pass through to Claude CLI for API configuration
+API_ENV_VARS = [
+    "ANTHROPIC_BASE_URL",
+    "ANTHROPIC_AUTH_TOKEN",
+    "API_TIMEOUT_MS",
+    "ANTHROPIC_DEFAULT_SONNET_MODEL",
+    "ANTHROPIC_DEFAULT_OPUS_MODEL",
+    "ANTHROPIC_DEFAULT_HAIKU_MODEL",
+]
+
 # Read-only feature MCP tools
 READONLY_FEATURE_MCP_TOOLS = [
     "mcp__features__feature_get_stats",
@@ -234,6 +244,9 @@ class AssistantChatSession:
         # Use system Claude CLI
         system_cli = shutil.which("claude")
 
+        # Build environment overrides for API configuration
+        sdk_env = {var: os.getenv(var) for var in API_ENV_VARS if os.getenv(var)}
+
         try:
             self.client = ClaudeSDKClient(
                 options=ClaudeAgentOptions(
@@ -246,6 +259,7 @@ class AssistantChatSession:
                     max_turns=100,
                     cwd=str(self.project_dir.resolve()),
                     settings=str(settings_file.resolve()),
+                    env=sdk_env,
                 )
             )
             await self.client.__aenter__()