feat(studio): hand an export straight to a social network

EXPORT only ever wrote a file, and posting it meant leaving the studio, finding
the file and uploading it again. The dialog now offers FACEBOOK, INSTAGRAM,
REDDIT and X beside the sizes, and the render goes to the network instead of the
download folder.

What the browser can do decides how, since a page may not touch another origin's
composer: a phone's share sheet opens the target app with the picture already
attached, a desktop gets the picture on the clipboard and the site in a new tab
for one paste, and an origin with no clipboard API downloads the file beside the
open site. The line under the row says so before the click.

docker/frontend/src/App.tsx

@@ -17,6 +17,7 @@ import { loadEngine, MARK_FACES } from './engine/assets';
 import { renderPhoto, type RenderAssets } from './engine/exportEngine';
 import { download, fileToBytes, readCapturedAt, readGps, readIso, readSpecs, resizedJpeg, scaledJpeg, type ShotSpecs } from './engine/imageOps';
 import { developRaw, isRawName } from './engine/rawDevelop';
+import { sharePhoto, type ShareSite } from './engine/share';
 import { heicToJpeg, isHeicName } from './engine/heicDevelop';
 import { clearRaw, readRaw, storeRaw } from './engine/rawStore';
 import { getPhoto, loadEdit, readPhotoFile, saveEdit, setRotation as savePhotoRotation } from './engine/library';
@@ -1748,7 +1749,7 @@ export function Workspace() {
 
   // `true` when a file was handed over, so CLEAR knows the export it offered
   // actually happened before the photo comes off the stage.
-  const exportPhoto = useCallback(async (target: number | null): Promise<boolean> => {
+  const exportPhoto = useCallback(async (target: number | null, share?: ShareSite): Promise<boolean> => {
     if (!engine || !source) return false;
     if (!pro && proLookInUse()) {
       promptPro();
@@ -1833,7 +1834,11 @@ export function Workspace() {
         source.bytes
       );
       const stamp = new Date().toISOString().replace(/[-:T]/g, '').slice(0, 14);
-      download(bytes, `recipescam_${(recipe.name || 'photo').replace(/\W+/g, '-').toLowerCase()}_${stamp}.jpg`);
+      const name = `recipescam_${(recipe.name || 'photo').replace(/\W+/g, '-').toLowerCase()}_${stamp}.jpg`;
+      // SHARE hands the same bytes to the browser's share sheet instead of the
+      // download folder, so the file never lands on the machine on the way out.
+      if (share) await sharePhoto(bytes, name, share);
+      else download(bytes, name);
       // The moment the app has done the visitor's work is the moment it has earned
       // a place on the machine: the install offer waits for this instead of
       // opening on the way in (which nobody reads).
@@ -4141,6 +4146,10 @@ export function Workspace() {
             setChoosingExport(false);
             void exportPhoto(target);
           }}
+          onShare={(site) => {
+            setChoosingExport(false);
+            void exportPhoto(null, site);
+          }}
           onClose={() => setChoosingExport(false)}
         />
       ) : null}