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/features/common-settings/general/RoomEncryption.tsx

@@ -121,7 +121,7 @@ export function RoomEncryption({ permissions }: RoomEncryptionProps) {
                     size="500"
                   >
                     <Box grow="Yes">
-                      <Text size="H4">Enable Encryption</Text>
+                      <Text as="h2" size="H4">Enable Encryption</Text>
                     </Box>
                     <IconButton size="300" onClick={() => setPrompt(false)} radii="300" aria-label="Cancel">
                       <Icon src={Icons.Cross} />