fix(providers): correct GLM API base URL to /api/paas/v4

* fix: add OpenAI-style tool_calls support for MiniMax and other providers

MiniMax and some other providers return tool calls in OpenAI's native
JSON format instead of ZeroClaw's XML-style <invoke> tag format.

This fix adds support for parsing OpenAI-style tool_calls:
- {"tool_calls": [{"type": "function", "function": {"name": "...", "arguments": "{...}"}}]}

The parser now:
1. First tries to parse as OpenAI-style JSON with tool_calls array
2. Falls back to ZeroClaw's original <invoke> tag format
3. Correctly handles the nested JSON string in the arguments field

Added 3 new tests covering:
- Single tool call in OpenAI format
- Multiple tool calls in OpenAI format
- Tool calls without content field

Fixes #226

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

* fix(providers): correct GLM API base URL to /api/paas/v4

The GLM (Zhipu) provider was using the incorrect base URL
`https://open.bigmodel.cn/api/paas` which resulted in 404 errors
when making API calls. The correct endpoint is
`https://open.bigmodel.cn/api/paas/v4`.

This fixes issue #238 where the agent would appear unresponsive
when using GLM-5 as the default model.

The fix aligns with the existing test `chat_completions_url_glm`
which already expected the correct v4 endpoint.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

---------

Co-authored-by: Claude Opus 4.6 <noreply@anthropic.com>

src/providers/mod.rs

@@ -194,7 +194,7 @@ pub fn create_provider(name: &str, api_key: Option<&str>) -> anyhow::Result<Box<
             "Z.AI", "https://api.z.ai/api/coding/paas/v4", key, AuthStyle::Bearer,
         ))),
         "glm" | "zhipu" => Ok(Box::new(OpenAiCompatibleProvider::new(
-            "GLM", "https://open.bigmodel.cn/api/paas", key, AuthStyle::Bearer,
+            "GLM", "https://open.bigmodel.cn/api/paas/v4", key, AuthStyle::Bearer,
         ))),
         "minimax" => Ok(Box::new(OpenAiCompatibleProvider::new(
             "MiniMax", "https://api.minimax.chat", key, AuthStyle::Bearer,