feat(a11y): label form controls + overlays (P3-4)

Accessible names for ~15 controls that lacked them: invite/join/create-room/
account-data/image-pack/private-note/power-level inputs (visible <label htmlFor>
where a label exists, else aria-label); the two range sliders (night-light
intensity, noise-gate threshold); the soundboard file input; media <video>
elements; and the Media Gallery (region) + Search (dialog) overlays. Hidden
notification/preview <audio> marked aria-hidden.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/components/AccountDataEditor.tsx

@@ -213,6 +213,7 @@ function AccountDataView({ type, defaultContent, onEdit }: AccountDataViewProps)
           <Text size="L400">Account Data</Text>
           <Input
             variant="SurfaceVariant"
+            aria-label="Account data type"
             size="400"
             radii="300"
             readOnly