feat(instance): the first start offers instances as tiles

Under the wordmark on a cobalt wash, two tiles as Proton's account page
shows its services: the build's instance, chosen in one tap, and
another, which unfolds the address to type. A ring from cobalt to
copper, a glow and a tagline come in under the pointer, on the
keyboard's focus, while pressed or open; without a mouse the taglines
always show. The launch screen's "Halkyon" over "Learn" becomes
BrandWordmark, which both show.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Signed-off-by: Tizian 「ティツィアーン」 <raisondetredev@pm.me>

halkyon_learn_flutter/lib/l10n/app_en.arb

@@ -665,6 +665,9 @@
   "instanceAddress": "Instance address",
   "instanceUseBuiltIn": "Use {name}",
   "@instanceUseBuiltIn": {"placeholders": {"name": {"type": "String"}}},
+  "instanceBuiltInTagline": "Comes with the app",
+  "instanceAnother": "Another instance",
+  "instanceAnotherTagline": "Enter its address",
   "instanceContinue": "Continue",
   "instanceAddressRequired": "Enter the address of an instance.",
   "instanceAddressInvalid": "This isn't an address.",