feat: redesign Insert tab and fix all warnings

- Redesign Insert ribbon tab with 6 groups matching screenshot layout:
  Reference (Attach/Clip/Adjust large + Underlay Layers/Frames/Snap small),
  Point Cloud (Attach), Block (Multi-View Block/Insert large + Create/Edit/Base small),
  Attributes (Define/Edit large + Manage/Sync small),
  Import (Import/Land XML), Content (Content Browser/Design Center)
- Remove Primitives group and dead box_prim/clear/cylinder/sphere modules
- Fix all compiler warnings with #[allow(dead_code)] on unused-but-intentional items

Co-Authored-By: Claude Sonnet 4.6 <[email protected]>

src/app/mod.rs

@@ -356,6 +356,7 @@ pub enum Message {
     LayoutContextMenuClose,
     // ── Layout Manager Panel ────────────────────────────────────────────
     LayoutManagerOpen,
+    #[allow(dead_code)]
     LayoutManagerClose,
     LayoutManagerSelect(String),
     LayoutManagerRenameBuf(String),
@@ -369,6 +370,7 @@ pub enum Message {
     SetTheme(Theme),
     // ── Keyboard Shortcut Editor ────────────────────────────────────────
     ShortcutsPanelOpen,
+    #[allow(dead_code)]
     ShortcutsPanelClose,
     /// Close the viewport right-click context menu without performing any action.
     ViewportContextMenuClose,
@@ -418,6 +420,7 @@ pub enum Message {
     PlotStyleClear,
     /// Open/close the Plot Style panel.
     PlotStylePanelOpen,
+    #[allow(dead_code)]
     PlotStylePanelClose,
     /// Select an ACI entry in the panel.
     PlotStylePanelSelectAci(u8),
@@ -433,6 +436,7 @@ pub enum Message {
     PlotStylePanelSavePath(Option<std::path::PathBuf>),
     // ── TextStyle Font Browser ────────────────────────────────────────────
     TextStyleDialogOpen,
+    #[allow(dead_code)]
     TextStyleDialogClose,
     TextStyleDialogSelect(String),
     TextStyleDialogSetCurrent,
@@ -446,12 +450,14 @@ pub enum Message {
     TextStyleFontPick(String),
     // ── TableStyle Dialog ─────────────────────────────────────────────────
     TableStyleDialogOpen,
+    #[allow(dead_code)]
     TableStyleDialogClose,
     TableStyleDialogSelect(String),
     TableStyleDialogNew,
     TableStyleDialogDelete,
     // ── MLineStyle Dialog ─────────────────────────────────────────────────
     MlStyleDialogOpen,
+    #[allow(dead_code)]
     MlStyleDialogClose,
     MlStyleDialogSelect(String),
     MlStyleDialogSetCurrent,