refactor(ci): use marker comments instead of regex for tracker workflow

Add TRACKER: HTML comment markers to COMPATIBILITY.md, README.md, and
all 5 translation READMEs. Rewrite gitea-tracker.yml to use grep -n
for precise line-based insertion and sed line-address editing.

Markers introduced:
- TRACKER:QUICK-REF-MAX  — Quick Reference max tested version
- TRACKER:VERSION-INSERT — Version History row insertion point
- TRACKER:LATEST-VERIFIED — latest verified note version
- TRACKER:BADGE — shields.io badge version
- TRACKER:LATEST-TESTED — latest tested version in READMEs

Co-Authored-By: Claude <noreply@anthropic.com>

docs/README.ja.md

@@ -58,7 +58,7 @@ cd tools && go run . dev
 ## 互換性
 
 - **Gitea 1.25+** — v1.25で導入されたメールテンプレートディレクトリ構造
-- **最新テスト:** Gitea 1.26.4
+- **最新テスト:** Gitea 1.26.4<!-- TRACKER:LATEST-TESTED -->
 - Gitea公式テンプレートと100%互換 — 詳細は [COMPATIBILITY.md](COMPATIBILITY.md)を参照
 
 ## ライセンス