refactor(application): filter_rules.py 更名 rules.py 并合并 RuleHelper

规则域收敛为单一事实来源 app/application/rules.py：
- filter_rules.py 更名为 rules.py（内置规则集 + RuleParser）
- filter.py 仅含 66 行 RuleHelper（用户规则组配置访问），并入 rules.py
- 同步更新 5 处引用方导入、nettest stub 目标与架构文档
- 兼容映射 app.helper.rule 指向新路径，legacy 导入仍可用

app/modules/filter/__init__.py

@@ -5,11 +5,11 @@ from typing import List, Tuple, Union, Dict, Optional
 
 from app.domain.context import TorrentInfo, MediaInfo
 from app.domain.metainfo import MetaInfo, clear_rust_parse_options_cache, _rust_parse_options
-from app.application.filter import RuleHelper
+from app.application.rules import RuleHelper
 from app.runtime.log import logger
 from app.modules import _ModuleBase
-from app.application.filter_rules import RuleParser
-from app.application.filter_rules import BUILTIN_RULE_SET
+from app.application.rules import RuleParser
+from app.application.rules import BUILTIN_RULE_SET
 from app.schemas.types import ModuleType, OtherModulesType, SystemConfigKey
 from app.adapters.system import rust as rust_accel
 from app.foundation import size as size_tools