Refactor filter configuration with regex validation

- Add regex validation utility for query strings
- Update filter_config_service to use regex validation
- Add comprehensive test coverage for regex validator
- Update exception handling for validation errors
- Update documentation for tasks

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

backend/app/exceptions.py

@@ -256,6 +256,56 @@ class FilterInvalidRegexError(BadRequestError):
         return {"pattern": self.pattern, "error": self.error}
 
 
+class FilterRegexTooLongError(BadRequestError):
+    """Raised when a regex pattern exceeds the maximum length."""
+
+    error_code: str = "filter_regex_too_long"
+
+    def __init__(self, pattern: str, max_length: int) -> None:
+        """Initialize with the pattern and maximum allowed length.
+
+        Args:
+            pattern: The regex pattern that is too long.
+            max_length: The maximum allowed length.
+        """
+        self.pattern = pattern
+        self.max_length = max_length
+        self.actual_length = len(pattern)
+        super().__init__(
+            f"Regex pattern exceeds maximum length of {max_length} characters: "
+            f"{self.actual_length} provided"
+        )
+
+    def get_error_metadata(self) -> dict[str, str | int | float | bool | None]:
+        return {
+            "pattern_length": self.actual_length,
+            "max_length": self.max_length,
+        }
+
+
+class FilterRegexTimeoutError(BadRequestError):
+    """Raised when a regex pattern compilation times out (possible ReDoS attack)."""
+
+    error_code: str = "filter_regex_timeout"
+
+    def __init__(self, pattern: str, timeout_seconds: int) -> None:
+        """Initialize with the pattern and timeout value.
+
+        Args:
+            pattern: The regex pattern that timed out.
+            timeout_seconds: The timeout value in seconds.
+        """
+        self.pattern = pattern
+        self.timeout_seconds = timeout_seconds
+        super().__init__(
+            f"Regex pattern compilation timed out after {timeout_seconds}s "
+            f"(possible ReDoS attack). Pattern is too complex or causes catastrophic backtracking."
+        )
+
+    def get_error_metadata(self) -> dict[str, str | int | float | bool | None]:
+        return {"timeout_seconds": self.timeout_seconds}
+
+
 class JailNotFoundInConfigError(NotFoundError):
     """Raised when the requested jail name is not defined in any config file."""