Release v0.54.0-nightly.20260728.gbef611950

What's Changed

• fix(a2a-server): normalize CRLF line endings to LF in getProposedContent by @luisfelipe-alt in #28531
• fix(core): enforce explicit tag length and validation in file keychain by @luisfelipe-alt in #28523

Full Changelog: v0.54.0-nightly.20260727.g3818efbbf...v0.54.0-nightly.20260728.gbef611950