Atomic state and hardened API defaults

State writes become atomic, API defaults get locked down, and Go 1.25 is standardized.

A quiet reliability release:

  • Atomic JSON state writes — container state files can no longer be left

half-written if the process dies mid-save.

  • Isolated tests — the test suite runs against CARDINAL_DATA_DIR instead

of a shared real home directory.

  • Secured API defaults — Bearer authentication enabled by default, with

image metadata stored safely.

  • Standardized toolchain — Go 1.25 across CI and release tooling.

Nothing flashy, but it's the kind of hardening that keeps a container runtime

dependable in production.