test: add comprehensive unit tests — coverage 20.2% → 91.8%

Add 12 test files covering all internal packages:

- internal/util/util_test.go (97.2%)
- internal/model/model_test.go (100.0%)
- internal/config/config_test.go (88.1%)
- internal/template/builtin_test.go (98.8%)
- internal/middleware/middleware_test.go (98.7%)
- internal/database/repo_extra_test.go (85.5%)
- internal/rules/converter_test.go (99.1%)
- internal/service/subscription_test.go (75.7%)
- internal/handler/handler_test.go (90.6%)
- internal/filter/filter_extra_test.go (91.9%)
- internal/proxy/client_parser_test.go (96.1%)
- internal/render/render_extra_test.go (99.2%)

Overall: 91.8% (4033/4400 statements) — exceeds 85% acceptance threshold.
All tests pass, go vet clean, go build clean.

AGENTS.md

@@ -13,6 +13,7 @@ SUB STORE 项目重构
 开发前必读 [`docs/review-resolutions.md`](docs/review-resolutions.md) — 45 条 review 问题的逐条决议（ProxyNode 类型、token 双哈希、SQLite PRAGMA、sing-box 完整结构等）。开发中不得偏离已定决议；如需变更，先改本文档再改代码。
 
 **关键决议摘要**：
+
 - ProxyNode = `map[string]any`，深拷贝用 json.Marshal/Unmarshal
 - token 校验先 SHA-256 再 ConstantTimeCompare（防长度泄露时序攻击）
 - SQLite: WAL + busy_timeout=5000 + foreign_keys=ON + MaxOpenConns=1
@@ -20,7 +21,12 @@ SUB STORE 项目重构
 - custom 规则链上限 32 条，替代 JS script 过滤器
 - modernc.org/sqlite（纯 Go），接受写性能 tradeoff
 
+## 验收标准
+
+- 单元测试覆盖率 ≥ 85%
+
 <!-- CODEGRAPH_START -->
+
 ## CodeGraph
 
 This project has a CodeGraph MCP server (`codegraph_*` tools) configured. CodeGraph is a tree-sitter-parsed knowledge graph of every symbol, edge, and file. Reads are sub-millisecond and return structural information grep cannot.
@@ -29,17 +35,17 @@ This project has a CodeGraph MCP server (`codegraph_*` tools) configured. CodeGr
 
 Use codegraph for **structural** questions — what calls what, what would break, where is X defined, what is X's signature. Use native grep/read only for **literal text** queries (string contents, comments, log messages) or after you already have a specific file open.
 
-| Question | Tool |
-|---|---|
-| "Where is X defined?" / "Find symbol named X" | `codegraph_search` |
-| "What calls function Y?" | `codegraph_callers` |
-| "What does Y call?" | `codegraph_callees` |
-| "What would break if I changed Z?" | `codegraph_impact` |
-| "Show me Y's signature / source / docstring" | `codegraph_node` |
-| "Give me focused context for a task/area" | `codegraph_context` |
-| "Survey an unfamiliar module/topic" | `codegraph_explore` |
-| "What files exist under path/" | `codegraph_files` |
-| "Is the index healthy?" | `codegraph_status` |
+| Question                                      | Tool                |
+| --------------------------------------------- | ------------------- |
+| "Where is X defined?" / "Find symbol named X" | `codegraph_search`  |
+| "What calls function Y?"                      | `codegraph_callers` |
+| "What does Y call?"                           | `codegraph_callees` |
+| "What would break if I changed Z?"            | `codegraph_impact`  |
+| "Show me Y's signature / source / docstring"  | `codegraph_node`    |
+| "Give me focused context for a task/area"     | `codegraph_context` |
+| "Survey an unfamiliar module/topic"           | `codegraph_explore` |
+| "What files exist under path/"                | `codegraph_files`   |
+| "Is the index healthy?"                       | `codegraph_status`  |
 
 ### Rules of thumb
 
@@ -51,5 +57,6 @@ Use codegraph for **structural** questions — what calls what, what would break
 
 ### If `.codegraph/` doesn't exist
 
-The MCP server returns "not initialized." Ask the user: *"I notice this project doesn't have CodeGraph initialized. Want me to run `codegraph init -i` to build the index?"*
+The MCP server returns "not initialized." Ask the user: _"I notice this project doesn't have CodeGraph initialized. Want me to run `codegraph init -i` to build the index?"_
+
 <!-- CODEGRAPH_END -->