feat(inspect): native Inspect a file page

#/inspect is now the concept's "Inspect a file" page instead of the legacy
handoff. One chosen or dropped image or video previews inline, and the one
heading action, "Open file metadata", opens the shared viewer with the full
inspector on a record read entirely in this browser. Nothing is uploaded,
imported or stored; only an explicit Send crosses the host bridge.

- inspect.mjs mounts the concept DOM (surface, file-drop, #local-preview)
  under the shell heading, owns one local session and the shared viewer and
  prompt sender, and releases media before the session revokes its URL on
  replacement, route change, page leave and dispose (D60-D65).
- A file that cannot be read after choosing opens the inspector's
  unreadable state when the browser declares a supported type, instead of
  the "unsupported" copy; the local adapter maps a browser read failure to
  an unreadable record.
- The route is native; Overview keeps its card to the legacy metadata page,
  which is unchanged.
- workspace-inspect.spec.mjs covers the chooser and viewer rail against the
  Images rail for the same bytes, drop, cancel and reselect, unsupported and
  unreadable files, video, URL ownership, mid-read replacement, exact send
  and the no-request/no-storage rule.

web/workspace.html

@@ -12,6 +12,7 @@
     <script src="lib/viewerjs/viewer.min.js" defer></script>
     <script src="js/comfy-metadata.js" defer></script>
     <script src="js/gallery-settings.js" defer></script>
+    <script src="js/png-metadata.js" defer></script>
     <script type="module" src="js/workspace/index.mjs"></script>
 </head>
 <body class="ca-tools">