Introduce a conditional `trusted=yes` setting for the Raspberry Pi
repository in the Dockerfile when `DEBIAN_SUITE=trixie`. This bypasses
SHA1 signature rejection by trixie's apt system using Sequoia. Ensure
that bookworm maintains full signature verification. Updated
documentation to explain the trixie-specific caveat.
Introduce `DEBIAN_SUITE` as a configurable argument in the Dockerfile, build
script, and CI workflow to align kernel builds with the target Raspberry Pi
OS release. Updated documentation to clarify the relationship between
suite versions and kernel compatibility.
