Move STATUS_VARIANT out of the "use client" SessionsTable module

The session detail page (a server component) was importing STATUS_VARIANT
from SessionsTable.tsx, a "use client" file. Next.js compiles client
modules separately for the server and client bundles, and pulling a plain
value (not a component) across that boundary let the two compiler caches
drift out of sync in dev, so the same session status could render a
different Badge color depending on which page rendered it. Moved the
constant into its own plain module that both files import.

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01WzyfRyA7h5rs5SCAahLAWd

components/sessions/session-status.ts

@@ -0,0 +1,8 @@
+// Plain data, deliberately kept out of SessionsTable.tsx (a "use client"
+// module) so server components (e.g. the session detail page) can import it
+// without pulling a value across the client/server compilation boundary.
+export const STATUS_VARIANT = {
+  active: "default",
+  completed: "secondary",
+  aborted: "destructive",
+} as const;