Co-locate CadCommand impls with their ribbon toolbar modules

Each command implementation is now in the same file as its ribbon
tool definition. Groups moved to a dedicated groups/ toolbar folder.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/modules/home/select.rs

@@ -0,0 +1,62 @@
+// SelectObjectsCommand — generic "select objects then run command" gather phase.
+//
+// Used when a modify command is invoked with nothing pre-selected.
+// The user may single-click, box-select, or polygon-select any number of objects.
+// After the FIRST completed selection action (regardless of method) the command fires
+// immediately — no Enter required.
+
+use acadrust::Handle;
+use glam::Vec3;
+
+use crate::command::{CadCommand, CmdResult};
+use crate::scene::wire_model::WireModel;
+
+pub struct SelectObjectsCommand {
+    pending_cmd: String,
+}
+
+impl SelectObjectsCommand {
+    pub fn new(pending_cmd: &str) -> Self {
+        Self {
+            pending_cmd: pending_cmd.to_string(),
+        }
+    }
+}
+
+impl CadCommand for SelectObjectsCommand {
+    fn name(&self) -> &'static str {
+        "SELECT"
+    }
+
+    fn prompt(&self) -> String {
+        format!("{}  Select objects:", self.pending_cmd)
+    }
+
+    // Opt into the selection-gathering path; host routes clicks through
+    // the normal selection system and calls on_selection_complete after each action.
+    fn is_selection_gathering(&self) -> bool {
+        true
+    }
+
+    fn on_selection_complete(&mut self, handles: Vec<Handle>) -> CmdResult {
+        if handles.is_empty() {
+            return CmdResult::NeedPoint;
+        }
+        CmdResult::Relaunch(std::mem::take(&mut self.pending_cmd), handles)
+    }
+
+    // These are never called while is_selection_gathering is true, but the
+    // trait requires implementations.
+    fn on_point(&mut self, _pt: Vec3) -> CmdResult {
+        CmdResult::NeedPoint
+    }
+    fn on_enter(&mut self) -> CmdResult {
+        CmdResult::Cancel
+    }
+    fn on_escape(&mut self) -> CmdResult {
+        CmdResult::Cancel
+    }
+    fn on_hover_entity(&mut self, _handle: Handle, _pt: Vec3) -> Vec<WireModel> {
+        vec![]
+    }
+}