fix(security-guards): sync gitignore guard with the Cover_*.* and cv/*.txt rules

Two personal-data ignore rules existed in .gitignore but not in
REQUIRED_IGNORE_RULES, so a change weakening either would have passed CI:
cover_letters/Cover_*.* (the uppercase naming variant /apply recognizes)
and cv/*.txt (ATS text extractions of tailored CVs).

Also: regression tests pinning #252's ragged-row bounds fix in
convert_salary_excel.py (mutation-verified), and removal of the vestigial
cover_letters/OpenFonts/cover.cls, which since #252's rename ambiguously
declared the same class as the real cover.cls (zero references; cover
letter re-compiled and page-verified after removal).

Guard-list gap surfaced by CodeRabbit's review on jakob1379's Nix demo
fork PR (jakob1379/ai-job-search#1).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>

tools/security_guards.py

@@ -50,7 +50,11 @@ REQUIRED_IGNORE_RULES = [
     "**/job_scraper/seen_jobs.json",
     "cv/main_*.*",
     "!cv/main_example.tex",
+    # ATS text extractions (/apply step 5d) carry the CV's full text.
+    "cv/*.txt",
     "cover_letters/cover_*.*",
+    # /apply also recognizes the uppercase Cover_* naming variant.
+    "cover_letters/Cover_*.*",
     "documents/cv/**",
     "documents/linkedin/**",
     "documents/diplomas/**",