feat: add unified_review MCP prompt + sync tool/prompt counts

Adds the unified_review MCP prompt (invoked as /code-review-graph:unified_review)
that drives the unified-review workflow: graph context -> detect_changes ->
score_review -> findings -> dedupe_findings -> generate_report. READ-ONLY:
every finding waits for a manual fix decision. Takes base and tier
(fast/standard/strict) arguments.

- prompts.py: unified_review_prompt + docstring count 5->6
- main.py: @mcp.prompt() registration
- tests/test_prompts.py: TestUnifiedReviewPrompt + preamble test
- docs: LLM-OPTIMIZED-REFERENCE, COMMANDS, CLAUDE.md, INDEX, architecture,
  README + 4 localized READMEs; tool count 30->31 and prompt count 5->6
  synced (historical ROADMAP/FEATURES version notes left unchanged)

README.zh-CN.md

@@ -253,8 +253,8 @@ code-review-graph serve            # 启动 MCP 服务器
 | `list_repos_tool` | 列出已注册的仓库 |
 | `cross_repo_search_tool` | 跨所有注册仓库搜索 |
 
-**MCP 提示模板**（5 种工作流模板）：
-`review_changes`、`architecture_map`、`debug_issue`、`onboard_developer`、`pre_merge_check`
+**MCP 提示模板**（6 种工作流模板）：
+`review_changes`、`architecture_map`、`debug_issue`、`onboard_developer`、`pre_merge_check`、`unified_review`
 
 </details>