chore: bump version to 4.5.0

Bug fixes:
- Fix inverted pager detection logic (returned error instead of path)
- Fix repo.Clone ignoring destination directory parameter
- Fix sheet loading using append on pre-sized slices
- Clean up partial files on copy failure
- Trim whitespace from editor config

Security:
- Add path traversal protection for cheatsheet names

Performance:
- Move regex compilation outside search loop
- Replace string concatenation with strings.Join in search

Build:
- Remove go:generate; embed config and usage as string literals
- Parallelize release builds
- Add fuzz testing infrastructure

Testing:
- Improve test coverage from 38.9% to 50.2%
- Add fuzz tests for search, filter, tags, and validation

Documentation:
- Fix inaccurate code examples in HACKING.md
- Add missing --conf and --all options to man page
- Add ADRs for path traversal, env parsing, and search parallelization
- Update CONTRIBUTING.md to reflect project policy

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

internal/sheet/testdata/fuzz/FuzzSearchCatastrophicBacktracking/3ad1cae1b78a2478

@@ -0,0 +1,4 @@
+go test fuzz v1
+string("0")
+int(-6)
+int(5)

internal/sheet/testdata/fuzz/FuzzSearchRegex/74c0a5e8e3464bfd

@@ -0,0 +1,3 @@
+go test fuzz v1
+string(".")
+string(" 0000\n\n\n\n00000")