feat(select): Select Similar + Quick Select panel (#28)

Two ways to extend the current selection by entity type + layer:

* `Select Similar` (right-click → Select Similar, or `SELECTSIMILAR` /
  `SELSIM`): for every (type, layer) pair in the current selection, add
  every entity in the active layout that matches the pair. The seed
  selection stays selected; matches already selected are not
  double-counted.
* `Quick Select` (right-click → Quick Select…, or `QSELECT` / `QS`):
  opens a centred floating panel with Object-type and Layer pick_lists
  (populated only with values that actually exist in the active layout)
  and an "Append to current selection" checkbox. `(Any)` in either slot
  skips that filter. Apply replaces the selection (or extends it with
  Append on) and reports the match count on the command line. Cancel,
  Esc, and outside-click all dismiss without applying. When opened with
  a selection present, the panel pre-fills both filters from the first
  selected entity so QSelect doubles as an editable Select Similar.

Scoped to entities owned by the active layout's block-record so a paper
layout's QSELECT never reaches into model-space entities (and vice
versa). Entity-type names live in a single `entity_type_name` helper in
`entities::traits` to keep the UI strings and the filter keys aligned.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/app/commands.rs

@@ -1738,6 +1738,17 @@ impl OpenCADStudio {
                 self.refresh_properties();
             }
 
+            "SELECTSIMILAR" | "SELSIM" => {
+                let added = self.tabs[i].scene.select_similar();
+                self.command_line
+                    .push_output(&format!("Select Similar: {} added.", added));
+                self.refresh_properties();
+            }
+
+            "QSELECT" | "QS" => {
+                return Task::done(Message::QSelectOpen);
+            }
+
             // ── LIST — entity info ────────────────────────────────────────
             "LIST" | "LI" => {
                 let selected: Vec<_> = self.tabs[i].scene.selected_entities();