feat(deploy): add multi-route support [SLIP-74]

[mitchelljphayes]

Support multiple HTTP routes per app — multiple Caddy hostnames mapping to different containers/ports within a single deploy.

• RouteEntry/RepoRouteEntry structs, routes: Vec on both configs
• ReverseProxy trait: set_routes/remove_routes with @id = slip-{app}-{index}
• Backward compat: old set_route/remove_route delegate to new methods
• MergedRoute: pair server hostnames with repo ports/containers by index
• Pod mode: routes target containers by name
• AppRuntimeState.current_routes for state tracking
• Preview multi-route subdomain support
• Route reconciliation handles multiple routes per app
• Validation: ambiguous configs, missing hostnames
• 24 new tests (371 total)

SLIP-74