Fix ribbon active state, polar snap, FILLET pick mode, and arc preview plane

- Deactivate ribbon tool highlight when command ends (issue #1)
- Reset last_point on new command dispatch to fix polar snap offset (issue #2)
- FILLET/CHAMFER: disable text input during entity pick so clicks reach viewport (issue #3)
- Dropdown icon buttons now use RibbonToolClick so they highlight blue when active
- FILLET/CHAMFER: AutoCAD-style sub-step UX — typing R/D + Enter prompts for value
- Fix FILLET arc preview plane: arc was rendering in XZ instead of XY
- Bump version to 0.1.1

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

src/ui/ribbon/mod.rs

@@ -103,6 +103,9 @@ impl Ribbon {
     pub fn activate_tool(&mut self, id: &str) {
         self.active_tool = Some(id.to_string());
     }
+    pub fn deactivate_tool(&mut self) {
+        self.active_tool = None;
+    }
     pub fn set_wireframe(&mut self, w: bool) {
         self.wireframe = w;
     }