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/routers/settings.py

@@ -6,6 +6,7 @@ API endpoints for global settings management.
 Settings are stored in the registry database and shared across all projects.
 """
 
+import os
 import sys
 from pathlib import Path
 
@@ -33,6 +34,11 @@ def _parse_yolo_mode(value: str | None) -> bool:
     return (value or "false").lower() == "true"
 
 
+def _is_glm_mode() -> bool:
+    """Check if GLM API is configured via environment variables."""
+    return bool(os.getenv("ANTHROPIC_BASE_URL"))
+
+
 @router.get("/models", response_model=ModelsResponse)
 async def get_available_models():
     """Get list of available models.
@@ -54,6 +60,7 @@ async def get_settings():
     return SettingsResponse(
         yolo_mode=_parse_yolo_mode(all_settings.get("yolo_mode")),
         model=all_settings.get("model", DEFAULT_MODEL),
+        glm_mode=_is_glm_mode(),
     )
 
 
@@ -71,4 +78,5 @@ async def update_settings(update: SettingsUpdate):
     return SettingsResponse(
         yolo_mode=_parse_yolo_mode(all_settings.get("yolo_mode")),
         model=all_settings.get("model", DEFAULT_MODEL),
+        glm_mode=_is_glm_mode(),
     )