fix: resolve nested SSH Include paths relative to their file (#747)

[MisterTea]

Resolves relative Include directives from the containing config file, preserves absolute paths, and retains wildcard subdirectories for nested includes. Adds focused helper regressions and preserves unrelated local edits.

Closes #747.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 79.38%. Comparing base (db4f6f6) to head (43eeedc).
⚠️ Report is 13 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #840      +/-   ##
==========================================
+ Coverage   79.26%   79.38%   +0.11%     
==========================================
  Files         118      121       +3     
  Lines       12633    12779     +146     
  Branches     8143     8232      +89     
==========================================
+ Hits        10014    10144     +130     
- Misses       1552     1571      +19     
+ Partials     1067     1064       -3     

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