fix: reachable undo, nameable groups, and no favicon request

Found by running the app in a browser for the first time.

- Undo was only reachable from the team tab, and only after a team solve had
  finished, so an equip made from the character view had no way back. Both
  views now show it whenever there is something to undo.
- The owner-group naming dropdown listed all 23 espers from the game database
  rather than the characters the capture says you own. Two espers are both
  published as "Zero", so the list held two identical entries and picking the
  wrong one misattributed a whole loadout; conversely a character the game
  database has never heard of had no entry at all and its group could not be
  named. Options now come from the captured roster, labelled with the esper
  name and disambiguated by codename when two owned characters share one.
- An inline SVG favicon, so the page stops requesting one that does not exist.
  Inline rather than a file because the single-file build must make no
  requests at all.

Verified headless against the real 819-item export: import writes 819 items,
20 characters and 99 equipment rows to IndexedDB; a solve runs in a real
Worker and scores 0.6690 for Zankou, matching the Node bench; equip writes 8
app rows and displaces 7; undo restores all 99 imported rows; state survives
a reload. The file:// build renders, imports, solves inline and issues no
network request.

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

index.html

@@ -3,6 +3,7 @@
   <head>
     <meta charset="utf-8" />
     <meta name="viewport" content="width=device-width, initial-scale=1" />
+    <link rel="icon" href="data:image/svg+xml,<svg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 32 32'><rect width='32' height='32' rx='6' fill='%230d1117'/><rect x='6' y='6' width='9' height='9' fill='%23e5534b'/><rect x='17' y='6' width='9' height='9' fill='%23d9b125'/><rect x='6' y='17' width='9' height='9' fill='%234c8ed9'/><rect x='17' y='17' width='9' height='9' fill='%232ea44f'/></svg>" />
     <title>NTE gear optimizer</title>
   </head>
   <body>