feat(studio): rich theme picker (presets + custom colour) + editor 0.11.0

Settings dialog's Theme Plugin section is now a grid of
swatched tiles:

- Built-in (none) — falls back to FaiTheme.light/.dark
- One tile per installed studio.theme.* plugin, each
  showing the plugin's primary/secondary/tertiary as
  live colour dots. Tile loads its preview lazily so a
  dozen installed themes don't block the picker.
- Custom — opens a colour-picker dialog with 12 curated
  Material presets + a hex input + live preview. Selecting
  applies ColorScheme.fromSeed for both brightnesses.

main.dart's _pluginThemes parses a 'custom:#RRGGBB' sigil
in the same notifier slot as plugin capability ids, so the
existing persistence + restoration paths cover the custom
case with no new state.

Bumps editor to 0.11.0 (type-checked port connections +
dynamic card width fix + card-height border allowance) and
Studio to 0.58.0.

Signed-off-by: flemming-it <stefan.a.flemming@googlemail.com>

lib/l10n/app_de.arb

@@ -108,6 +108,12 @@
   "themePluginNone": "Standard (kein Plugin)",
   "themePluginHint": "Installiertes studio.theme.*-Plugin auswählen, um das ganze Studio umzustylen. Erst eines aus dem Store installieren.",
   "themePluginEmpty": "Kein Theme-Plugin installiert. Im Store eines aus der Kategorie studio-plugin auswählen.",
+  "themePluginCustom": "Eigene Farbe",
+  "themePluginCustomDialogTitle": "Eigenes Theme — Seedfarbe wählen",
+  "themePluginCustomHexLabel": "Hex-Farbe",
+  "themePluginCustomPreview": "Live-Vorschau",
+  "themePluginCustomCancel": "Abbrechen",
+  "themePluginCustomApply": "Anwenden",
   "settingsTitle": "Hub-Endpunkt",
   "settingsHost": "Host",
   "settingsPort": "Port",