fix: escape JSON in <script>; popup player picks edited if available

P1: views were emitting <%- JSON.stringify(...) %> directly inside <script>
tags. A video title like "</script><script>alert(1)</script>" would break
out of the script and inject HTML. Added res.locals.jsonForScript() that
escapes <, >, &, U+2028, U+2029 before output and switched all three
templates (op/editor.ejs, op/folder.ejs, folder.ejs) to use it.

P2: The internal popup player in /folder/:name always hit
/api/video/:id/file which returned the original. Made the file endpoint
default to the edited variant when present and only fall back to original
when ?edited=0 is given. Editor page passes ?edited=0 explicitly so the
operator always re-trims from the original. Standalone /player/:id no
longer needs the ?edited=1 hint.

Verified: rendered editor HTML escapes </script> payloads to \u003c/script,
default file endpoint serves edited.mp4 while ?edited=0 serves original.mp4.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

views/folder.ejs

@@ -43,7 +43,7 @@
   </div>
 
   <script>
-    window.__SITE__ = { folder: <%- JSON.stringify(folder) %> }
+    window.__SITE__ = { folder: <%- jsonForScript(folder) %> }
   </script>
   <script src="/static/player.js"></script>
 </body>