fix(theseus/aegis): retire bchwallet on every launch + branded dock/list icon

Two follow-ups from the on-device test.

Two Aegis addons showing up (bchwallet + aegis):
- migrateAegisRename previously only ran when addons/aegis/ didn't exist,
  which meant any bchwallet copy the signed OTA update endpoint reinstalls
  after the first migration stays there forever, and AddonHost loads both
  as separate wallets. Rewritten to always retire addons/bchwallet/ when
  it's present, regardless of whether aegis/ is already installed. The
  storage-copy (bchwallet.json → aegis.json) still only runs the first
  time so a downgrade doesn't clobber fresh 0.4+ state.
- Also flushes any stray addons/siawallet/ that comes back the same way.

Sidebar dock and Extensions list icons showed the raw 🛡 emoji:
- chrome.html's dock-button renderer and settings.html's extensions-list
  renderer now accept `data:image/svg+xml…` values for manifest.icon and
  render them as <img> instead of text. Emoji strings still render as
  before.
- aegis addon.json's icon is now the exact hex-aspis mark from
  aegis.x/brand/favicon.svg (URL-encoded inline). Version bumped to
  0.4.1 so seedBundledAddons reseeds the new addon.json on next launch.

addon.json

@@ -1,10 +1,10 @@
 {
   "id": "aegis",
   "name": "Aegis Wallet",
-  "version": "0.4.0",
+  "version": "0.4.1",
   "description": "Multi-chain wallet (BCH, BTC, TRX, ETH, SOL, SC, DGB) derived from your Theseus vault. Dapps get window.bitcoincash on .x sites; window.tronWeb / window.tronLink / window.ethereum / window.solana on any https page.",
   "author": "Silent Mode",
-  "icon": "🛡",
+  "icon": "data:image/svg+xml;utf8,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 32 32' fill='none'%3E%3Cpolygon points='16,2 28,9 28,23 16,30 4,23 4,9' fill='%230a0a0d' stroke='%23D6FF3D' stroke-width='1.6' stroke-linejoin='round'/%3E%3Ccircle cx='16' cy='16' r='4.5' fill='none' stroke='%23D6FF3D' stroke-width='1.4'/%3E%3Ccircle cx='16' cy='16' r='1.6' fill='%23D6FF3D'/%3E%3C/svg%3E",
   "main": "index.js",
   "capabilities": ["sidebar-panel", "vault-derive", "page-inject", "approval-modal"],
   "absorbs": ["bchwallet", "siawallet"],