Welcome page polish + ToS placeholder + made_fun text fix

- res/values/strings_en.arb: made_easy value 'made easy' -> 'made fun'.
  This is what AnimatedTypingText actually feeds (line 183 of
  create_pin_welcome_page.dart), not payment_made_easy which is unused
  in this rendering path.
- assets/images/cake_logo_{light,dark}.svg replaced with mark-only
  (hash_wallet/01_mark.svg — just the # in green box, no embedded
  wordmark). Welcome screen layout already renders 'Hash Wallet' text
  next to this image; the previous wordmark-embedded SVG caused the
  duplicate 'Hash Wallet [...] Hash Wallet' you screenshot'd. Mark
  alone is theme-agnostic (green box with white # works on both light
  and dark backgrounds), so light + dark use the same file.
- assets/images/welcome_{dark,light}_theme.svg: gradient bottom stop
  faded to transparent. Eliminates the hard cutoff edge where the
  sky-rect ended and flat surface color began — the SVG now blends
  smoothly into the page background.
- assets/text/Terms_of_Use.txt: replaced 188-line Cake Labs LLC legal
  document with a Hash Wallet placeholder (same pattern as PRIVACY.md).
  Real ToS pending legal review.

res/values/strings_en.arb

@@ -602,7 +602,7 @@
   "long_press_show_balance": "Long press card to show balance",
   "low_fee": "Low fee",
   "low_fee_alert": "You currently are using a low network fee priority. This could cause long waits, different rates, or canceled trades. We recommend setting a higher fee for a better experience.",
-  "made_easy": "made easy",
+  "made_easy": "made fun",
   "manage_nodes": "Manage nodes",
   "manage_pow_nodes": "Manage PoW nodes",
   "manage_providers": "Manage providers",