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>

components/businesses/BusinessForm.tsx

@@ -17,6 +17,7 @@ import { fonts, spacing } from "@/constants/theme";
 import { useAppTheme } from "@/contexts/ThemeContext";
 import type { ThemeColors } from "@/lib/theme-palette";
 import { useThemedStyles } from "@/lib/use-themed-styles";
+import { isRequiredString } from "@/lib/form-validation";
 import { api } from "@/lib/trpc";
 
 type BusinessFormValues = {
@@ -153,10 +154,7 @@ export function BusinessForm({
   }
 
   function handleSave() {
-    if (!values.name.trim()) {
-      setFieldError("Business name is required");
-      return;
-    }
+    if (!canSave) return;
 
     const payload = buildPayload();
 
@@ -186,6 +184,8 @@ export function BusinessForm({
   }
 
   const saving = createBusiness.isPending || updateBusiness.isPending;
+  const nameError = values.name.trim() ? undefined : "Business name is required";
+  const canSave = isRequiredString(values.name);
 
   return (
     <KeyboardAvoidingView
@@ -199,7 +199,13 @@ export function BusinessForm({
         keyboardShouldPersistTaps="handled"
       >
         <Card title="Profile">
-          <Input label="Name" value={values.name} onChangeText={(v) => patch("name", v)} />
+          <Input
+            label="Name"
+            value={values.name}
+            onChangeText={(v) => patch("name", v)}
+            required
+            error={nameError}
+          />
           <Input
             label="Nickname"
             value={values.nickname}
@@ -281,6 +287,7 @@ export function BusinessForm({
           <Button
             title={mode === "create" ? "Create business" : "Save changes"}
             loading={saving}
+            disabled={!canSave}
             onPress={handleSave}
           />
           {mode === "edit" ? (