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/form-validation.ts

@@ -0,0 +1,66 @@
+import { useCallback, useState } from "react";
+
+export function useFieldVisibility() {
+  const [touched, setTouched] = useState<Record<string, boolean>>({});
+  const [submitted, setSubmitted] = useState(false);
+
+  const touch = useCallback((field: string) => {
+    setTouched((prev) => (prev[field] ? prev : { ...prev, [field]: true }));
+  }, []);
+
+  const visible = useCallback(
+    (field: string) => submitted || Boolean(touched[field]),
+    [submitted, touched],
+  );
+
+  const markSubmitted = useCallback(() => setSubmitted(true), []);
+
+  return { touch, visible, markSubmitted };
+}
+
+export function isRequiredString(value: string): boolean {
+  return value.trim().length > 0;
+}
+
+export function isValidEmail(value: string): boolean {
+  const trimmed = value.trim();
+  if (!trimmed) return false;
+  return /^[^\s@]+@[^\s@]+\.[^\s@]+$/.test(trimmed);
+}
+
+export function isValidPassword(value: string): boolean {
+  return value.length >= 8;
+}
+
+/** Parses a non-negative decimal, or null if empty/invalid. */
+export function parseNonNegativeNumber(value: string): number | null {
+  const trimmed = value.trim();
+  if (!trimmed) return null;
+  const n = Number(trimmed);
+  if (Number.isNaN(n) || n < 0) return null;
+  return n;
+}
+
+export function isValidTaxRate(value: string): boolean {
+  const n = parseNonNegativeNumber(value);
+  if (n === null) return false;
+  return n <= 100;
+}
+
+export type LineItemInput = {
+  description: string;
+  hours: string;
+  rate: string;
+};
+
+export function validateLineItems(items: LineItemInput[]): string | null {
+  if (items.length === 0) return "Add at least one line item";
+
+  for (const item of items) {
+    if (!isRequiredString(item.description)) return "Each line needs a description";
+    if (parseNonNegativeNumber(item.hours) === null) return "Hours must be a valid number";
+    if (parseNonNegativeNumber(item.rate) === null) return "Rate must be a valid number";
+  }
+
+  return null;
+}