Add bounding-box object alignment (ALIGNLEFT/TOP/etc.), ported from Mac2CAM

Six one-shot alignment commands for the current selection —
ALIGNLEFT/ALIGNHCENTER/ALIGNRIGHT/ALIGNTOP/ALIGNVCENTER/ALIGNBOTTOM —
distinct from the existing point-picking ALIGN/ALIGN3D command: each
nudges every selected object (or complete group, via new
Scene::selected_object_units) so its bounding-box edge/center lines up
with the extreme edge/center already present in the selection, closer
to a word processor's "align objects" than AutoCAD's 3-point ALIGN.

Wired as plain one-click Tool entries in the Modify extension panel,
next to the existing ALIGN entry, matching that panel's flat-list
convention (no point prompts, so no dropdown submenu needed).

Co-Authored-By: Claude Sonnet 5 <[email protected]>

src/ui/ribbon/modify_panel.rs

@@ -37,6 +37,47 @@ pub(super) const TOOLS: &[Tool] = &[
         icon: include_bytes!("../../../assets/icons/modify_align.svg"),
         options: &[],
     },
+    // ALIGNLEFT/ALIGNHCENTER/ALIGNRIGHT/ALIGNTOP/ALIGNVCENTER/ALIGNBOTTOM:
+    // one-shot bounding-box alignment of the current selection — distinct
+    // from "ALIGN" above (point-picked 3D placement). No point prompts, so
+    // each is a plain one-click Tool rather than a dropdown submenu, matching
+    // this panel's existing flat-list convention.
+    Tool {
+        command: "ALIGNLEFT",
+        label: "Align Left",
+        icon: include_bytes!("../../../assets/icons/align_left.svg"),
+        options: &[],
+    },
+    Tool {
+        command: "ALIGNHCENTER",
+        label: "Align Horizontal Centers",
+        icon: include_bytes!("../../../assets/icons/align_hcenter.svg"),
+        options: &[],
+    },
+    Tool {
+        command: "ALIGNRIGHT",
+        label: "Align Right",
+        icon: include_bytes!("../../../assets/icons/align_right.svg"),
+        options: &[],
+    },
+    Tool {
+        command: "ALIGNTOP",
+        label: "Align Top",
+        icon: include_bytes!("../../../assets/icons/align_top.svg"),
+        options: &[],
+    },
+    Tool {
+        command: "ALIGNVCENTER",
+        label: "Align Vertical Centers",
+        icon: include_bytes!("../../../assets/icons/align_vcenter.svg"),
+        options: &[],
+    },
+    Tool {
+        command: "ALIGNBOTTOM",
+        label: "Align Bottom",
+        icon: include_bytes!("../../../assets/icons/align_bottom.svg"),
+        options: &[],
+    },
     Tool {
         command: "BREAK",
         label: "Break",