refactor: move WAL corruption metric to periodic stats worker counting broken .docs files

[eguguchkin]

• I have read and followed all requirements in CONTRIBUTING.md;
• I used LLM/AI assistance to make this pull request;

[codecov-commenter]

Codecov Report

❌ Patch coverage is 53.33333% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 70.79%. Comparing base (bcaaf48) to head (726a14d).

Files with missing lines	Patch %	Lines
fracmanager/fracmanager.go	57.14%	4 Missing and 2 partials ⚠️
frac/active.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #433      +/-   ##
==========================================
- Coverage   70.82%   70.79%   -0.04%     
==========================================
  Files         225      225              
  Lines       17487    17498      +11     
==========================================
+ Hits        12386    12387       +1     
- Misses       4179     4187       +8     
- Partials      922      924       +2     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.
• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.