v1.2.0

Manual-install robustness: defensive preflight, honest failure reporting, clear
actionable errors, and Ubuntu 26.04 support. Validated by real installs on
Ubuntu 24.04 and 26.04.

Added

• Ubuntu 26.04 support. Preflight now admits 22.04/24.04/26.04 (was a
  hard block on anything but 22.04/24.04). A unified /etc/os-release parser
  (ID + VERSION_ID) replaces the two divergent parsers; a genuinely-unsupported
  OS fails with a message naming the detected OS + the supported set. Validated:
  a full install on Ubuntu 26.04 reaches a Ready control-plane node (k8s 1.35.4,
  containerd 2.2.2).
• Preflight checks with clear remedies: not-root, CPU arch (amd64/arm64),
  swap enabled, required ports in use (6443/10250/2379/2380/6446 + udp
  51820/8472), clock/NTP skew, and Nodeward host:port reachability (classifies
  DNS-fail vs refused vs firewall). Cheap/local checks run before network ones.

Fixed

• Honest failure reporting (the "install said success but the node never came
  up" bug). The on-node installer now checks the exit code of every step
  (register + install were previously unchecked) and only prints the success
  banner if all passed; otherwise it prints a FAILED: <step> block and exits
  non-zero. The install/register cobra commands now exit non-zero on failure
  (were exit 0), log.Fatalf/panic on recoverable errors are replaced with a
  structured FAILED: <step> — Cause — Try block, and gRPC registration errors
  map to actionable messages (bad/expired token, bad --aid, Nodeward
  unreachable).
• Register flag validation: empty/missing --token/--aid/--server are
  rejected up front (an empty --server no longer silently persists an empty
  Nodeward host).