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/app/commands/blocks.rs

@@ -486,6 +486,7 @@ impl OpenCADStudio {
             // BLOCKPALETTE / BLOCKSPALETTE — toggle the docked Insert Block panel.
             "BLOCKPALETTE" | "BLOCKSPALETTE" => {
                 self.show_block_palette ^= true;
+                self.ribbon.set_block_palette(self.show_block_palette);
                 if self.show_block_palette {
                     // Always open expanded so the panel is immediately usable;
                     // the user can still collapse it via the pin (Auto) button.

src/app/update/dialog.rs

@@ -597,6 +597,7 @@ pub(super) fn on_ribbon_tool_click(&mut self, tool_id: String, event: ModuleEven
                 match id {
                     PanelId::BlockPalette => {
                         self.show_block_palette = false;
+                        self.ribbon.set_block_palette(false);
                         self.block_palette.placing = None;
                     }
                     PanelId::Properties => {