feat(ribbon): Block Palette button reflects panel open state

The Insert tab's Block Palette button now behaves like the View tab toggles
(UCS Icon, View Cube, Ortho, Properties, File Tabs, Layout Tabs): it stays
highlighted while the block palette panel is open and clears when closed.

The Ribbon gains a show_block_palette flag with a set_block_palette setter,
fed into ToggleState and mapped in is_active_tool for the BLOCKPALETTE tool
id. show_block_palette on the app remains the single source of truth; both
mutation paths now mirror it onto the ribbon:

- BLOCKPALETTE / BLOCKSPALETTE command toggles ribbon state alongside the
  panel (src/app/commands/blocks.rs).
- Closing the panel via the dock rail close button clears the ribbon state,
  matching how Close(Properties) already syncs (src/app/update/dialog.rs).

src/ui/ribbon/widgets.rs

@@ -37,6 +37,7 @@ pub(super) struct ToggleState {
     pub show_viewcube: bool,
     pub show_ucs_icon: bool,
     pub show_properties: bool,
+    pub show_block_palette: bool,
     pub show_file_tabs: bool,
     pub show_layout_tabs: bool,
 }
@@ -359,6 +360,7 @@ pub(super) fn is_active_tool(
         "NAVVCUBE" => state.show_viewcube,
         "UCSICON" => state.show_ucs_icon,
         "PROPERTIES" => state.show_properties,
+        "BLOCKPALETTE" => state.show_block_palette,
         "FILETAB" => state.show_file_tabs,
         "LAYOUTTAB" => state.show_layout_tabs,
         id => active_tool.as_deref() == Some(id),