Separated doc link checker from daily tests

[Copilot]

Doc link failures were triggering the same notification email as real test failures, making it hard to distinguish signal from noise.

Changes

• New daily_doc_link_check.yml workflow — moves DocLinkCheck into its own standalone workflow with a dedicated NotifyOnFailure job (distinct email subject/body pointing to the new workflow URL); adds explicit least-privilege permissions blocks
• daily_tests.yml — removes DocLinkCheck job; simplifies NotifyOnFailure to only watch DailyTests
• README.md — adds a separate badge for the new doc link check workflow

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.86%. Comparing base (f29fa00) to head (4184fdc).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #369   +/-   ##
=======================================
  Coverage   85.86%   85.86%           
=======================================
  Files          41       41           
  Lines        1662     1662           
=======================================
  Hits         1427     1427           
  Misses        235      235           

Flag	Coverage Δ
unittests	85.86% <ø> (ø)

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