build: ship LICENSE and NOTICE in every package and image

The RPM, DEB and APK payloads carried no license material at all, and
the OCI image copied LICENSE and CREDITS but not NOTICE. For an AGPL
distribution that is not defensible packaging. Every delivery channel
now carries the same license set:

- nfpm packages install LICENSE and NOTICE under /usr/share/doc/silo/.
  The entries are declared once per packager because nfpm only honors
  type: license on rpm and silently drops such entries from deb and apk
  -- the rpm keeps its %license flag, deb and apk carry plain files at
  the same path. CREDITS stays out of the OS packages deliberately: at
  1.8MB it would dominate an otherwise ~40MB payload.
- The OCI image gains /licenses/NOTICE next to the existing LICENSE and
  CREDITS, in the Dockerfile and in both context-staging paths (the
  make docker target and docker-release.yml).
- The GoReleaser archives list their files explicitly; the default
  globs would keep missing NOTICE.

NOTICE's first line now reads 2015-2025 to match the banner constants
fixed in b57275be3 -- it had kept upstream's stale 2015-2023 claim --
and verify-rebrand.sh pins both NOTICE copyright lines.

The payload locks move in the same commit: sign-release-rpms.sh expects
the six-file listing, and the test-release validation asserts presence,
count, the rpm %license flag, and sha256 equality of the packaged
LICENSE and NOTICE against the repository files across all three
formats and both architectures.

Also dropped the unit's WorkingDirectory=/usr/local, a leftover from
upstream's /usr/local/bin install layout. Debian policy 9.1.2 keeps
packages out of /usr/local entirely; the binary already installs to
/usr/bin and the service does not depend on its working directory.

Verified locally with nfpm v2.47.0 (the CI-pinned version): built all
six packages via package-release.sh, then ran the test-release
validation step verbatim (extracted from the workflow YAML) and the
signing script's payload comparison against them in an Ubuntu 24.04
container -- both pass. Built the arm64 image from the real
Dockerfile.goreleaser and confirmed /licenses holds CREDITS, LICENSE
and NOTICE. make rebrand-guard passes with the new NOTICE pins.

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Signed-off-by: Feng Ruohang <rh@vonng.com>

silo.service

@@ -9,8 +9,6 @@ AssertFileIsExecutable=/usr/bin/silo
 [Service]
 Type=notify
 
-WorkingDirectory=/usr/local
-
 User=silo
 Group=silo
 ProtectProc=invisible