Fix Live Activity lock screen rendering and polish multi-account auth.

Flatten widget layouts and use system colors so banner and expanded regions render on vibrant lock screens; migrate auth sessions per account to prevent double sign-in; scope app lock PIN to accounts; default clock description to "Clock In"; add architecture docs and deferred form validation on auth screens.

Co-authored-by: Cursor <cursoragent@cursor.com>

lib/time-clock.ts

@@ -4,6 +4,13 @@ export type ClockOutOutcome =
   | "saved_no_client"
   | "zero_hours";
 
+export const DEFAULT_CLOCK_DESCRIPTION = "Clock In";
+
+export function resolveClockDescription(description: string | null | undefined): string {
+  const trimmed = description?.trim();
+  return trimmed || DEFAULT_CLOCK_DESCRIPTION;
+}
+
 export function formatElapsedSeconds(seconds: number): string {
   const h = Math.floor(seconds / 3600);
   const m = Math.floor((seconds % 3600) / 60);