feat(miner-packaging): add version/compatibility check on gittensory-miner startup

[JSONbored]

Add a startup compatibility check to the gittensory-miner CLI mirroring the existing gittensory-mcp package's upgrade-nudge pattern (checking the npm registry for a newer published version and printing an upgrade command if the installed version is stale), so a fleet of miner instances doesn't silently drift onto incompatible shared-engine versions once @jsonbored/gittensory-engine is published. Pure CLI/packaging concern; does not implement the shared engine package itself (that's tracked separately).

Deliverables

• On any gittensory-miner invocation, a non-blocking async check against the npm registry (GITTENSORY_NPM_REGISTRY_URL override, same env var name convention as the mcp package) for a newer published @jsonbored/gittensory-miner version.
• If stale, print a one-line upgrade nudge (npm install -g @jsonbored/gittensory-miner@latest) without blocking or failing the current command.
• Respect a --no-update-check/GITTENSORY_MINER_NO_UPDATE_CHECK=1 opt-out for offline/air-gapped fleet operators.
• Network failures during the check (offline machine) must be silently swallowed — never crash the CLI because the registry was unreachable.
• Unit tests: stale version prints the nudge; current version prints nothing; a simulated network failure does not throw or block command execution; the opt-out env var/flag suppresses the check entirely.

References

• packages/gittensory-mcp/bin/gittensory-mcp.js lines 13-17 — the existing packageVersion/npmRegistryUrl/upgradeCommand pattern to mirror exactly.
• packages/gittensory-miner/ package (this extends its CLI, scaffolded in the packaging-skeleton issue).

[linear-code]

JSO-2428