Fix web file pickers and settings links not opening

[wassgha]

Summary

Fixes the web-only report where browse never opens a file dialog (DnD still works), settings links do nothing, and Chrome shows no “popups blocked” indicator.

Root causes addressed:

1. File pickers used display: none inputs + synthetic input.click(). That pattern fails in some Chromium setups; drag-and-drop still works. Upload / transcript import now use label-activated sr-only inputs.
2. Import transcript deferred input.click() to requestAnimationFrame, which drops the user gesture so Chrome never shows the dialog. The picker now opens in the same turn as the click.
3. Settings links could be covered by the popover dismiss backdrop when it stayed in-tree while the panel was portaled (stacking-context mismatch). The backdrop is portaled with the panel, and settings anchors stop pointer propagation so dismiss logic cannot swallow the navigation.

Test plan

• On web (Chrome): click the upload dropzone / “browse” — OS file picker opens
• Drag-and-drop a media file onto the dropzone still works
• Open Import transcript from the source menu — file picker opens immediately
• Open Settings → click Discord / GitHub / X / Report an issue — each opens in a new tab
• Appearance toggle in Settings still works; clicking outside still dismisses the menu
• In the editor, Import on the transcript bar still opens a picker
• Desktop (Electron) menus / file flows still behave (backdrop still covers drag regions)