feat(ui): a question mark that keeps a section's explanation one tap away

HelpButton, beside a section's or a setting's title: the explanation opens
in a small dialog, under its title where given, rather than standing in the
everyday view (the developer's review of 3 Nov 2026). FieldInfoButton's
tooltip stays for a field's short hint.

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

packages/halkyon_ui/lib/l10n/halkyon_ui_de.arb

@@ -1,6 +1,5 @@
 {
   "@@locale": "de",
-
   "brand": "Halkyon",
   "close": "Schließen",
   "cancel": "Abbrechen",
@@ -17,5 +16,6 @@
   "copiedToClipboard": "In die Zwischenablage kopiert",
   "copy": "Kopieren",
   "paletteColorName": "{name, select, carrot{Karotte} cerise{Kirschrot} cobalt{Kobalt} copper{Kupfer} enzian{Enzian} fern{Farn} forest{Wald} ocean{Ozean} olive{Olive} pacific{Pazifik} pickle{Essiggurke} pine{Kiefer} pink{Rosa} plum{Pflaume} purple{Lila} reef{Riff} sahara{Sahara} slateblue{Schieferblau} soil{Erde} strawberry{Erdbeere} other{{name}}}",
-  "colorPickerLabel": "Farbe: {color}"
+  "colorPickerLabel": "Farbe: {color}",
+  "explain": "Was ist das?"
 }