feat: add web search block functionality and integrate with existing plugins

- Introduced a new web search block plugin to handle web search queries and results.
- Updated copilot, doc block, and pro block plugins to include web search context in AI completions.
- Implemented utility functions for parsing and building web search markdown.
- Enhanced API to support web search requests and responses.
- Added configuration for web search URL and timeout settings.
- Updated size limit checks to account for web search content.

backend/job_system.py

@@ -25,6 +25,7 @@ TERMINAL_EVENTS = {"done", "error", "cancelled"}
 JOB_TYPES = (
     "completion",
     "pro_completion",
+    "web_search",
     "compress",
     "ocr",
     "convert",
@@ -35,6 +36,7 @@ JOB_TYPES = (
 DEFAULT_CONCURRENCY = {
     "completion": 2,
     "pro_completion": 1,
+    "web_search": 1,
     "compress": 1,
     "ocr": 1,
     "convert": 1,
@@ -45,6 +47,7 @@ DEFAULT_CONCURRENCY = {
 DEFAULT_QUEUE_SIZE = {
     "completion": 16,
     "pro_completion": 8,
+    "web_search": 4,
     "compress": 8,
     "ocr": 8,
     "convert": 8,
@@ -54,11 +57,42 @@ DEFAULT_QUEUE_SIZE = {
 
 
 class JobSystemError(RuntimeError):
-    pass
+    """任务系统内部错误"""
+
+    def __init__(self, message: str = "任务系统错误", error_code: str = "job_system_error") -> None:
+        super().__init__(message)
+        self.message = message
+        self.error_code = error_code
+
+    def __str__(self) -> str:
+        return f"{self.error_code}: {self.message}"
 
 
 class QueueFullError(JobSystemError):
-    pass
+    """任务队列已满"""
+
+    def __init__(self, job_type: str, max_queue: int) -> None:
+        super().__init__(f"{job_type} 队列已满 (当前: {max_queue}/{max_queue})", "queue_full")
+        self.job_type = job_type
+        self.max_queue = max_queue
+
+
+# 修复：添加完整的异常类实现
+class JobSystemError(RuntimeError):
+    def __init__(self, message: str = "任务系统错误", error_code: str = "job_system_error") -> None:
+        super().__init__(message)
+        self.message = message
+        self.error_code = error_code
+
+    def __str__(self) -> str:
+        return f"{self.error_code}: {self.message}"
+
+
+class QueueFullError(JobSystemError):
+    def __init__(self, job_type: str, max_queue: int) -> None:
+        super().__init__(f"{job_type} 队列已满 (当前: {max_queue}/{max_queue})", "queue_full")
+        self.job_type = job_type
+        self.max_queue = max_queue
 
 
 @dataclass(frozen=True)