feat(ucs): interactive UCS command — UCS Z 90 typable everywhere (F2, #169)

Bare `UCS` now enters an interactive front-end (UcsCommand) that gathers the
option then its value as separate steps, instead of the command line
submitting `UCS` alone on the first Space. The front-end delegates execution
back to the existing inline `UCS <option> …` handler via a new
`CmdResult::Dispatch(String)`, so the coordinate-system math and the
save/persist path are untouched.

Now `UCS Z 90` works the same from the command line (Space-separated),
headless automation, and any source that feeds the active command — closing
the input half of #169. Inline `UCS Z 90` (one-shot / paste) still hits the
inline handler directly.

Second phase of routing input sources through the unified step driver: the
interactive command is driven by feed_command like any tool. Adds headless
test ucs_interactive_inline_args.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/app/automation.rs

@@ -565,6 +565,27 @@ mod tests {
         assert_eq!(app.automation_op(r#"{"op":"run"}"#)["ok"], false);
     }
 
+    #[test]
+    fn ucs_interactive_inline_args() {
+        // `UCS Z 90` must drive the interactive UCS command step-by-step (option
+        // "Z" then value "90") and rotate the active UCS 90° about Z. (#169)
+        let mut app = OpenCADStudio::new_for_test();
+        app.automation_op(r#"{"op":"new"}"#);
+        app.automation_op(r#"{"op":"run","cmd":"UCS Z 90"}"#);
+        let i = app.active_tab;
+        let ucs = app.tabs[i]
+            .active_ucs
+            .as_ref()
+            .expect("UCS Z 90 should set an active UCS");
+        // 90° about Z sends the X axis (1,0,0) → (0,1,0).
+        assert!(
+            ucs.x_axis.x.abs() < 1e-6 && (ucs.x_axis.y - 1.0).abs() < 1e-6,
+            "x_axis after UCS Z 90 = ({}, {})",
+            ucs.x_axis.x,
+            ucs.x_axis.y
+        );
+    }
+
     #[test]
     fn save_then_open_round_trips() {
         let mut app = OpenCADStudio::new_for_test();