fix(a11y): semantic headings, htmlFor/id associations, remove duplicate aria-labels

H-tag: add as=h1/h2 to dialog/UIA/auth headings (21 components)
Label: add htmlFor/id to PasswordRegisterForm (5 pairs) and PasswordResetForm (3 pairs)
Dupe: remove duplicate aria-label from Controls.tsx screenshare button, MembersDrawer, Members, RoomInput

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/app/components/DeviceVerification.tsx

@@ -259,7 +259,7 @@ export function DeviceVerification({ request, onExit }: DeviceVerificationProps)
           <Dialog variant="Surface">
             <Header style={DialogHeaderStyles} variant="Surface" size="500">
               <Box grow="Yes">
-                <Text size="H4">Device Verification</Text>
+                <Text as="h2" size="H4">Device Verification</Text>
               </Box>
               <IconButton size="300" radii="300" onClick={handleCancel} aria-label="Cancel verification">
                 <Icon src={Icons.Cross} />