feat(api): add GET /assets/:id/hires endpoint for original file download

Returns presigned S3 URL + filename/ext/file_size for the original
hi-res source so the Premiere plugin can download and import it.

services/mam-api/src/routes/assets.js

@@ -434,7 +434,7 @@ router.delete('/:id', async (req, res, next) => {
   }
 });
 
-// GET /:id/stream - Signed URL for proxy playback
+// GET /:id/stream - URL for proxy playback (relative path, for browser use)
 router.get('/:id/stream', async (req, res, next) => {
   try {
     const { id } = req.params;
@@ -483,6 +483,31 @@ router.get('/:id/video', async (req, res, next) => {
   } catch (err) { next(err); }
 });
 
+// GET /:id/hires - Presigned S3 URL for the original hi-res source file
+//
+// Returns a short-lived presigned URL that the Premiere plugin can use to
+// download the full-resolution original directly from S3.  Also includes
+// the derived filename and file_size so the client can show a size warning.
+router.get('/:id/hires', async (req, res, next) => {
+  try {
+    const { id } = req.params;
+    const r = await pool.query(
+      'SELECT original_s3_key, filename, display_name, file_size FROM assets WHERE id = $1',
+      [id]
+    );
+    if (r.rows.length === 0) return res.status(404).json({ error: 'Asset not found' });
+    const a = r.rows[0];
+    if (!a.original_s3_key) {
+      return res.status(404).json({ error: 'No hi-res source available for this asset' });
+    }
+    const url   = await getSignedUrlForObject(a.original_s3_key);
+    const parts = a.original_s3_key.split('.');
+    const ext   = (parts.length > 1 ? parts[parts.length - 1] : 'mxf').toLowerCase();
+    const base  = (a.display_name || a.filename || id).replace(/[^\w.-]/g, '_').substring(0, 100);
+    res.json({ url, filename: `${base}.${ext}`, ext, file_size: a.file_size || null, type: 'hires' });
+  } catch (err) { next(err); }
+});
+
 // GET /:id/thumbnail - Signed URL (JSON) or 302 redirect (?redirect=1) for thumbnail
 router.get('/:id/thumbnail', async (req, res, next) => {
   try {