Fix .gitignore: add .pytest_cache, htmlcov; update spec path

Author: alexander-vyh

.gitignore

@@ -54,10 +54,14 @@ test_data_*
 # PyInstaller specific
 *.manifest
 *.spec
-!fileshift.spec
+!packaging/fileshift.spec
 # Claude Code
 .claude/settings.local.json
 
+# Testing
+.pytest_cache/
+htmlcov/
+
 # Coverage
 .coverage
 coverage.xml