Adds a new wizard page (positioned right after Welcome, FreshInstall only)
that auto-runs EnvironmentCheckService on entry and shows one row per check
with status icon, localized title/message, and hint+help-link on
failure/unknown. A "Recheck" button re-runs it, guarded against re-entrancy.
IInstallerPage gets a BlocksNavigation default member; WizardViewModel's
Next button now binds to CanGoNext, which the current page can veto (used
here while a check run is in flight or a blocking Error+Failed result is
present — Warnings and Unknown results never block). The summary line names
the blocking checks so a disabled Next is self-explanatory.
Wires up DI for the check pipeline (IProcessRunner, IPortOwnerResolver,
per-run ClaudeCliLookup) and adds the checks.* / installer.systemCheck.*
locale keys in en.json + de.json.
Visual appearance is NOT verified — needs a manual pass in the running
installer.
