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/services/filter_config_service.py

@@ -21,6 +21,8 @@ from app.exceptions import (
     FilterInvalidRegexError,
     FilterNotFoundError,
     FilterReadonlyError,
+    FilterRegexTimeoutError,
+    FilterRegexTooLongError,
     JailNotFoundInConfigError,
 )
 from app.models.config import (
@@ -45,6 +47,7 @@ from app.utils.config_file_utils import (
     set_jail_local_key_sync,
 )
 from app.utils.jail_socket import reload_all
+from app.utils.regex_validator import RegexTimeoutError, validate_regex_pattern
 
 log: structlog.stdlib.BoundLogger = structlog.get_logger()
 
@@ -231,16 +234,30 @@ def _parse_filters_sync(
 def _validate_regex_patterns(patterns: list[str]) -> None:
     """Validate each pattern in *patterns* using Python's ``re`` module.
 
+    Checks each pattern for:
+    - Length limit (max 1000 characters)
+    - Compilation timeout (2 seconds) to prevent ReDoS attacks
+    - Syntax validity
+
     Args:
         patterns: List of regex strings to validate.
 
     Raises:
+        FilterRegexTooLongError: If any pattern exceeds 1000 characters.
+        FilterRegexTimeoutError: If compilation times out (possible ReDoS).
         FilterInvalidRegexError: If any pattern fails to compile.
     """
     for pattern in patterns:
         try:
-            re.compile(pattern)
+            validate_regex_pattern(pattern)
+        except ValueError as exc:
+            # Pattern length exceeded
+            raise FilterRegexTooLongError(pattern, max_length=1000) from exc
+        except RegexTimeoutError as exc:
+            # Pattern compilation timed out
+            raise FilterRegexTimeoutError(pattern, timeout_seconds=2) from exc
         except re.error as exc:
+            # Pattern syntax error
             raise FilterInvalidRegexError(pattern, str(exc)) from exc