feat(studio): add media properties panel for video/audio elements

Adds a new Media section to the Design panel that appears when a <video>
or <audio> element is selected. Controls include volume (slider),
playback rate, media start offset, loop/muted toggles, and for video:
object-fit, object-position, poster, and has-audio-track toggle.

Extends the source patcher with an "html-attribute" operation type for
native HTML attributes (loop, muted, poster) that don't use the data-
prefix. Adds coalesceKey to attribute commits so rapid slider/scrub
edits merge into a single undo entry.

packages/studio/src/hooks/useDomEditCommits.ts

@@ -190,6 +190,7 @@ export function useDomEditCommits({
   const {
     handleDomStyleCommit,
     handleDomAttributeCommit,
+    handleDomHtmlAttributeCommit,
     handleDomTextCommit,
     commitDomTextFields,
     handleDomTextFieldStyleCommit,
@@ -439,6 +440,7 @@ export function useDomEditCommits({
     resolveImportedFontAsset,
     handleDomStyleCommit,
     handleDomAttributeCommit,
+    handleDomHtmlAttributeCommit,
     handleDomTextCommit,
     commitDomTextFields,
     handleDomTextFieldStyleCommit,