brand: de-cake the app (hash-bag success art, asset + widget renames, filter, icon padding)

Send-success art: replace the Cake birthday cake with a Hash Bags money sack
that has a # on it and erupts #/$/₿ (assets/images/hash_bag.png). Used by the
success page, send-confirm sheet, exchange-trade, and dEURO savings.

Asset renames (files + refs):
- birthday_cake.png            -> hash_bag.png
- restore_cupcake(.png/_dark)  -> restore_hashbag.png
- qr-cake.png                  -> qr-hashbag.png
- arrow_bottom_cake_green.png  -> arrow_bottom_green.png (+ 2.0x/3.0x)

Identifier renames:
- CakeImageWidget -> HashImageWidget (widget + file + 93 refs)
- typography _cakeRegular/_cakeBold/_cakeSemiBold -> _hash*

Transaction filter: drop the Cake Pay "Orders" row and every non-Trocador
trade provider; the swap gate is already Trocador-only, so this just aligns the
filter UI with reality.

Android launcher: add breathing room to the adaptive-foreground # (all
densities, monochrome included); iOS icon unchanged.

About page: swap the Cake easter eggs for Hash Bags ones.

Deferred (needs a build to verify): new-ui .svg.vec filename renames
(cake_squircle_icon, cakewallet-wordmark, cake-setting) — already Hash Bags in
content, only the filenames are cake, and they route through the .vec precompile.

lib/utils/qr_util.dart

@@ -28,7 +28,7 @@ String getQrImage(WalletType type) {
       return 'assets/images/doge_chain_qr.svg';
     case WalletType.banano:
     case WalletType.none:
-      return 'assets/images/qr-cake.png';
+      return 'assets/images/qr-hashbag.png';
   }
 }