Add video picker and Discord video attachments.

The picker accepts one MP4 or WebM, the thread lightbox zooms photos, and Discord gets the video as a file on a follow-up message so photo embeds still render.

internal/web/posts_test.go

@@ -484,16 +484,19 @@ func TestQuestionPageRendersNestedPostControls(t *testing.T) {
 		`data-submit-button`,
 		`enctype="multipart/form-data"`,
 		`data-image-picker`,
-		`accept="image/jpeg,image/png,image/webp"`,
+		`accept="image/jpeg,image/png,image/webp,video/mp4,video/webm,.mp4,.webm"`,
 		`aria-live="polite"`,
 		`name="existing_image_id" value="root-photo"`,
 		`name="existing_image_id" value="reply-photo"`,
+		`data-image-zoom`,
+		`href="https://cdn.example/root-photo.jpg"`,
 		`src="https://cdn.example/root-photo.jpg"`,
 		`alt="Water pooling below the shutoff valve"`,
 		`src="https://cdn.example/reply-photo.png"`,
 		`alt="Photo attached to this post"`,
 		`src="https://cdn.example/admin-photo.webp"`,
 		`loading="lazy" decoding="async"`,
+		`data-image-zoom-dialog`,
 		`<figcaption>Replacement cartridge orientation</figcaption>`,
 		`action="/posts/` + root.ID + `/edit"`,
 		`action="/posts/` + homeownerReply.ID + `/edit"`,
@@ -556,6 +559,9 @@ func TestImagePickerAssetsAreServed(t *testing.T) {
 			path: "/static/app.js",
 			wants: []string{
 				`const pickerSelector = "[data-image-picker]"`,
+				`video/mp4`,
+				`video/webm`,
+				`showModal`,
 				`new DataTransfer()`,
 				`addEventListener("drop"`,
 				`resetImagePicker`,
@@ -569,6 +575,8 @@ func TestImagePickerAssetsAreServed(t *testing.T) {
 				`.image-dropzone:focus-within`,
 				`.image-preview-list`,
 				`.post-image-grid`,
+				`.post-video`,
+				`.image-zoom`,
 				`@media (max-width: 520px)`,
 			},
 		},