v2.80.0 — Self-upgrade

Self-upgrade

• great-cto upgrade --self — upgrades the CLI in place, detecting how it was
  installed from the running binary's realpath: npx cache (nothing to do — npx
  always runs latest), volta, pnpm, or npm with the exact global prefix derived
  from the binary path. On machines with more than one npm prefix it upgrades the
  binary that is actually running and prints which prefix was updated, then
  verifies old → new.
• Interactive update prompt — when a newer version exists and you're in a real
  terminal, the update hint becomes a one-time Update to X.Y.Z? [Y/n] (15s
  timeout = No, asked at most once per release via promptedFor in the cache).
  Non-TTY, CI, and protocol commands (mcp) keep the silent one-line hint, which
  now recommends great-cto upgrade --self.
• README highlights npx great-cto@latest as the zero-maintenance path for
  occasional use.
• Tests: CLI suite 229 → 264 (+35); board/root 198.

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