- CLAUDE.md: update error convention from core.E() to coreerr.E() to
match actual codebase usage
- Standardise go-log import alias from `core` to `coreerr` across 6
files (crypt/symmetric.go, crypt/kdf.go, crypt/crypt.go, crypt/hash.go,
crypt/checksum.go, crypt/openpgp/service.go) for consistency with the
11 files already using `coreerr`
- Fix shortenPackageName to handle all forge.lthn.ai/core/* module
prefixes instead of only cli/ and gui/, fixing TestShortenPackageName
Co-Authored-By: Virgil <virgil@lethean.io>