feat(studio): brand-agnostic onboarding hints + clickable checklist + theme-picker clarity

Three changes:

1. Onboarding checklist hints no longer mention DeepWiki,
   Semgrep, text.extract, or extract-summarize.yaml by
   name. Brand- and file-specific copy moved to neutral
   feature pointers ('add an MCP source', 'install a
   module'). Brand names belong on the welcome page only
   if they're load-bearing for understanding, which they
   aren't.

2. Checklist rows are now clickable. Tapping a row navigates
   to the page where the operator can complete it — MCP +
   AI open Settings, Module opens Store, Flow opens Flows.
   StudioShellState gains a public navigateTo(pageId) helper
   so descendants can drive sidebar selection without
   plumbing a controller through props.

3. Theme picker hint copy rewritten. Old hint suggested
   'Custom' was a single-colour tweak; new copy spells out
   that Material 3 derives a full palette (primary,
   secondary, tertiary, surface, …) from one seed colour.
   The Custom tile shows a small tune icon so its
   open-the-picker semantics is visually distinct from the
   apply-immediately plugin tiles.

Editor bumped to 0.12.0 (panel toggle + LabVIEW-style port
colours).

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

lib/l10n/app_localizations_en.dart

@@ -128,21 +128,21 @@ class AppLocalizationsEn extends AppLocalizations {
 
   @override
   String get welcomeChecklistMcpHint =>
-      'Store → Today hero, or Settings → MCP Clients. DeepWiki and Semgrep are one click each.';
+      'Add an MCP source from the Store, or configure one under Settings → MCP Clients.';
 
   @override
   String get welcomeChecklistModule => 'Install a text module';
 
   @override
   String get welcomeChecklistModuleHint =>
-      'Store → search \"text\" → Install. Try text.extract for PDFs and DOCX.';
+      'Install a module from the Store — pick whichever category fits your work. Modules are sandboxed F∆I components.';
 
   @override
   String get welcomeChecklistFlow => 'Run a saved flow';
 
   @override
   String get welcomeChecklistFlowHint =>
-      'Flows → pick one → Run. The bundled extract-summarize.yaml is a good first run.';
+      'Flows → pick one → Run. Studio ships a few demo flows; one of your own works too.';
 
   @override
   String get welcomeChecklistAllDone => 'All four steps complete.';
@@ -320,7 +320,7 @@ class AppLocalizationsEn extends AppLocalizations {
 
   @override
   String get themePluginHint =>
-      'Pick an installed studio.theme.* plugin to re-skin the whole app. Install one from the Store first.';
+      'Built-in and plugin tiles ship hand-curated palettes. The Custom tile derives a full Material 3 palette (primary, secondary, tertiary, surface, …) from one seed colour you pick — it\'s a complete theme, not a single-colour tweak.';
 
   @override
   String get themePluginEmpty =>