Migrated all Docker stages from Alpine 3.23 to Debian Trixie (13) to
address critical CVE in Alpine's gosu package and improve security
update frequency.
Key changes:
Updated CADDY_IMAGE to debian:trixie-slim
Added gosu-builder stage to compile gosu 1.17 from source with Go 1.25.6
Migrated all builder stages to golang:1.25-trixie
Updated package manager from apk to apt-get
Updated user/group creation to use groupadd/useradd
Changed nologin path from /sbin/nologin to /usr/sbin/nologin
Security impact:
Resolved gosu Critical CVE (built from source eliminates vulnerable Go stdlib)
Reduced overall CVE count from 6 (bookworm) to 2 (trixie)
Remaining 2 CVEs are glibc-related with no upstream fix available
All Go binaries verified vulnerability-free by Trivy and govulncheck
Verification:
E2E tests: 243 passed (5 pre-existing failures unrelated to migration)
Backend coverage: 87.2%
Frontend coverage: 85.89%
Pre-commit hooks: 13/13 passed
TypeScript: 0 errors
Refs: CVE-2026-0861 (glibc, no upstream fix - accepted risk)
