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_en.arb

@@ -111,6 +111,12 @@
   "themePluginNone": "Built-in (no plugin)",
   "themePluginHint": "Pick an installed studio.theme.* plugin to re-skin the whole app. Install one from the Store first.",
   "themePluginEmpty": "No theme plugins installed. Open the Store and pick one in the studio-plugin category.",
+  "themePluginCustom": "Custom colour",
+  "themePluginCustomDialogTitle": "Custom theme — pick a seed colour",
+  "themePluginCustomHexLabel": "Hex colour",
+  "themePluginCustomPreview": "Live preview",
+  "themePluginCustomCancel": "Cancel",
+  "themePluginCustomApply": "Apply",
   "settingsTitle": "Hub endpoint",
   "settingsHost": "Host",
   "settingsPort": "Port",