talm upgrade: make post-upgrade reconcile window configurable via a flag #190

The postUpgradeReconcileWindow constant is hardcoded at 90 seconds. The hint text emitted on a version mismatch even acknowledges this is too short for slow setups: "the node is slower than the 90s reconcile window — large image pulls or cold hardware can exceed it. Re-run talm get version after a minute to distinguish: if the version updated, the node was just slow".

An operator with known-slow hardware (cold OCI instances, large extensions: set, slow registry) should be able to widen the window for their environment without forking talm or running the manual check on every upgrade.

Scope: add --post-upgrade-reconcile-window <duration> to talm upgrade (default 90s for backward compatibility). Thread it through runPostUpgradeVersionVerifyInner, which already takes the window as a parameter. Reflect the active value in both the "waiting Xs for the node to finish booting..." line and the two-hypothesis hint so a custom window is self-documenting in the output.