chore(18-01): remove forecast route, sidebar entry, and revalidatePath calls (CLEAN-01)

- Remove Forecast NAV_ITEMS entry and TrendingUp import from AdminSidebar
- Delete src/app/admin/forecast/page.tsx and empty directory
- Remove revalidatePath("/admin/forecast") from assignOfferToProject, removeProjectOffer, updateProjectOfferTotal

src/app/admin/projects/project-actions.ts

@@ -135,14 +135,12 @@ export async function assignOfferToProject(formData: FormData) {
         : null,
   });
   revalidatePath(`/admin/projects/${parsed.data.project_id}`);
-  revalidatePath("/admin/forecast");
 }
 
 export async function removeProjectOffer(projectOfferId: string, projectId: string) {
   await requireAdmin();
   await db.delete(project_offers).where(eq(project_offers.id, projectOfferId));
   revalidatePath(`/admin/projects/${projectId}`);
-  revalidatePath("/admin/forecast");
 }
 
 export async function updateProjectOfferTotal(
@@ -158,5 +156,4 @@ export async function updateProjectOfferTotal(
     .set({ accepted_total: amount.toFixed(2) })
     .where(eq(project_offers.id, projectOfferId));
   revalidatePath(`/admin/projects/${projectId}`);
-  revalidatePath("/admin/forecast");
 }