rename: replace all user-facing 'Atlas' references with 'Vibn'

Updated UI text in: project-shell (tab label), AtlasChat (sender name),
FreshIdeaMain, TypeSelector, MigrateSetup, ChatImportSetup, FreshIdeaSetup,
CodeImportSetup, prd/page, build/page, projects/page, deployment/page,
activity/page, layout (page title/description), atlas-chat API route.
Code identifiers (AtlasChat component name, file names) unchanged.

Made-with: Cursor

components/layout/project-shell.tsx

@@ -23,7 +23,7 @@ interface ProjectShellProps {
 }
 
 const SECTIONS = [
-  { id: "overview",  label: "Atlas",     path: "overview" },
+  { id: "overview",  label: "Vibn",      path: "overview" },
   { id: "prd",       label: "PRD",       path: "prd" },
   { id: "build",     label: "Build",     path: "build" },
   { id: "growth",    label: "Growth",    path: "growth" },