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>

app/(app)/index.tsx

@@ -18,7 +18,7 @@ import { formatCurrency, formatDate } from "@/lib/format";
 import type { ThemeColors } from "@/lib/theme-palette";
 import { useThemedStyles } from "@/lib/use-themed-styles";
 import { getInvoiceStatus } from "@/lib/invoice-status";
-import { formatElapsedHoursMinutes } from "@/lib/time-clock";
+import { formatElapsedHoursMinutes, resolveClockDescription } from "@/lib/time-clock";
 import { useRunningElapsed } from "@/lib/use-running-elapsed";
 import { api } from "@/lib/trpc";
 
@@ -88,7 +88,7 @@ export default function DashboardScreen() {
                   <View style={styles.runningDot} />
                   <View style={styles.runningMeta}>
                     <Text style={styles.runningTitle}>
-                      {running.description || "Timer running"}
+                      {resolveClockDescription(running.description)}
                     </Text>
                     <Text style={styles.runningSub}>
                       {running.client?.name ?? "No client"}