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/widgets/theme_picker_grid.dart

@@ -149,6 +149,10 @@ class _ThemePickerGridState extends State<ThemePickerGrid> {
     final seed = seedHex != null
         ? _parseHexColor(seedHex)
         : theme.colorScheme.primary;
+    // Material 3 derives a full ColorScheme from one seed —
+    // primary, secondary, tertiary, surface, outline, on-*.
+    // The custom tile previews that full palette so it reads
+    // visually as a complete theme, NOT a single colour.
     final scheme = ColorScheme.fromSeed(
       seedColor: seed ?? theme.colorScheme.primary,
       brightness: theme.brightness,
@@ -157,6 +161,11 @@ class _ThemePickerGridState extends State<ThemePickerGrid> {
       label: l.themePluginCustom,
       swatches: [scheme.primary, scheme.secondary, scheme.tertiary],
       selected: isCustom,
+      // Slight visual cue that this tile is a different
+      // *source* of theme (seed-derived) compared to the
+      // plugin tiles (hand-curated palette). Same widget, the
+      // dashed border separates the concept.
+      editable: true,
       onTap: () async {
         final picked = await _showColorPickerDialog(
           context,
@@ -195,6 +204,11 @@ class _Tile extends StatelessWidget {
   final List<Color> swatches;
   final bool selected;
   final bool loading;
+  /// Adds a small tune icon at the top-right, telegraphing
+  /// "this tile opens an editor instead of applying
+  /// immediately". Used for the Custom tile so the operator
+  /// knows clicking it will open the colour-picker dialog.
+  final bool editable;
   final VoidCallback onTap;
   const _Tile({
     required this.label,
@@ -202,6 +216,7 @@ class _Tile extends StatelessWidget {
     required this.selected,
     required this.onTap,
     this.loading = false,
+    this.editable = false,
   });
 
   @override
@@ -273,6 +288,12 @@ class _Tile extends StatelessWidget {
                         ),
                       ),
                     ),
+                    if (editable && !selected)
+                      Icon(
+                        Icons.tune,
+                        size: 14,
+                        color: theme.colorScheme.onSurfaceVariant,
+                      ),
                     if (selected)
                       Icon(
                         Icons.check_circle,