feat(insert): add docked block palette

Add a searchable block palette with previews, file import, collision-safe nested definitions, and dependency/table-record import. Keep palette thumbnails current across drawing switches and block-definition edits.

src/modules/insert/mview_block.rs

@@ -1,9 +1,10 @@
 use crate::modules::{IconKind, ModuleEvent, ToolDef};
-pub const ICON: IconKind = IconKind::Svg(include_bytes!("../../../assets/icons/mview_block.svg"));
+pub const ICON: IconKind =
+    IconKind::Svg(include_bytes!("../../../assets/icons/blocks/insert.svg"));
 pub fn tool() -> ToolDef {
     ToolDef {
         id: "BLOCKPALETTE",
-        label: "Multi-View\nBlock",
+        label: "Block\nPalette",
         icon: ICON,
         event: ModuleEvent::Command("BLOCKPALETTE".to_string()),
     }