fix: guard against null billing plan cache entries

[TorstenDittmann]

Summary

• prevent getBasePlanFromGroup() from reading .group from falsy plan entries in the cached plans map
• avoid caching a null organizationPlan in the project layout on self-hosted installs
• fix the self-hosted billing plan lookup crash without changing broader billing behavior

[greptile-apps]

Greptile Summary

This PR fixes a crash on self-hosted installs by guarding two places where a null billing plan value could enter the plansInfo store and subsequently cause a runtime error.

• +layout.ts: The root cause — on self-hosted installs isCloud is false, so organizationPlan is always null. The previous code unconditionally called plansInfo.set(organization.billingPlanId, null) when the plan wasn't in the base-plans cache, inserting a null entry into a Map<string, Models.BillingPlan>. The fix adds an && organizationPlan guard that prevents the null write entirely.
• billing.ts: getBasePlanFromGroup() now uses a type predicate filter (plan): plan is Models.BillingPlan => !!plan && ... to skip falsy entries before accessing .group, acting as a defence-in-depth guard against any residual null values that may already be in the map.

Both changes are minimal, non-breaking, and correct — the added guards are transparent to cloud users where organizationPlan is always a real object.

Confidence Score: 5/5

Safe to merge — both changes are narrow null guards with no behavioral change for cloud installs.

No P0 or P1 issues found. The fix in +layout.ts correctly addresses the root cause (null being stored in a Map<string, Models.BillingPlan>), and the billing.ts fix adds a complementary defence-in-depth guard. Logic is unchanged for truthy organizationPlan values, so cloud behavior is unaffected.

No files require special attention — both changes are safe and well-scoped.

Important Files Changed

Filename	Overview
src/lib/stores/billing.ts	Adds a null/falsy type-guard in getBasePlanFromGroup's filter to prevent accessing .group on null plan entries
src/routes/(console)/project-[region]-[project]/+layout.ts	Guards plansInfo.set() with an organizationPlan truthiness check, preventing null from being cached into the plans map on self-hosted installs

_{Reviews (1): Last reviewed commit: "fix: guard against null billing plan cac..." | Re-trigger Greptile}