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/app/cmd_result.rs

@@ -290,6 +290,7 @@ impl H7CAD {
         if self.tabs[i].active_cmd.is_some() {
             self.focus_cmd_input()
         } else {
+            self.ribbon.deactivate_tool();
             self.blur_cmd_input()
         }
     }