Favicon, level file icons, and a feed error mark in the triangle's column

- The logo as favicon, squared up (it is 128x121), at /favicon.png and at
  /favicon.ico outside the auth layer, where a browser asking on its own got a
  401; an apple-touch-icon on white (#32).
- An item not yet downloaded had its download bar on a line of its own under the
  file icon, lifting the icon above its row's; the bar now sits under it without
  taking space (#31).
- A feed error is Font Awesome's exclamation, hung in the margin where a folder's
  triangle is, in the same column; a folder holding a failing feed has its
  triangle turn red.

Closes #31, #32.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

web/login.html

@@ -1,5 +1,6 @@
 <title>Sign in — iPodderX</title>
-<link rel="icon" href="/icon.png">
+<link rel="icon" type="image/png" sizes="128x128" href="/favicon.png">
+<link rel="apple-touch-icon" href="/apple-touch-icon.png">
 <style>
 /* Inter, from ipx itself; see the same rule in index.html. */
 @font-face{font-family:Inter;src:url(/inter.woff2) format("woff2");font-weight:100 900;font-display:swap}