feat(commandline): always-on keyboard capture + space submits like enter

Two behaviour changes that bring the command line in line with
established CAD workflow:

1. **Always-on keyboard capture.** The input was blurred whenever no
   command was running, so typed letters went nowhere until the user
   clicked into the field. Replace the blur with a re-focus on every
   command lifecycle transition (cmd_result.rs) and on viewport / tab
   / ribbon clicks (update.rs), focus the input at startup, and add
   a global key subscription that catches any unhandled character key
   or backspace and routes it into the buffer via two new messages
   (CommandAppendChar / CommandBackspace) — so the command line keeps
   accumulating keystrokes even if focus parks somewhere not
   focusable. Removes the unused blur_cmd_input helper.

2. **Space submits.** Typing a space at the end of the input now
   submits the buffer the same way Enter does. Only exception: an
   active command that's currently collecting free-form prose
   (TEXT / MTEXT / DDEDIT body, ATTDEF prompt / default value,
   INSERT attribute value, ATTEDIT cell). Those advertise the new
   `CadCommand::wants_text_with_spaces()` flag so the Space character
   reaches the buffer as a literal.

Co-Authored-By: Claude Opus 4.7 <[email protected]>

src/scene/pipeline/viewcube.rs

@@ -909,11 +909,11 @@ pub fn build_geometry() -> (Vec<CubeVertex>, Vec<u32>) {
         &mut is,
     );
     for &([sx, sy, sz], region) in &[
-        ([1.0f32, 1.0, 1.0], CORNER_TBK_R), // sy=+1 = BACK yönü
+        ([1.0f32, 1.0, 1.0], CORNER_TBK_R), // sy=+1 → BACK direction
         ([-1.0, 1.0, 1.0], CORNER_TBK_L),
         ([1.0, 1.0, -1.0], CORNER_BBK_R),
         ([-1.0, 1.0, -1.0], CORNER_BBK_L),
-        ([1.0, -1.0, 1.0], CORNER_TPF_R), // sy=-1 = FRONT yönü
+        ([1.0, -1.0, 1.0], CORNER_TPF_R), // sy=-1 → FRONT direction
         ([-1.0, -1.0, 1.0], CORNER_TPF_L),
         ([1.0, -1.0, -1.0], CORNER_BTF_R),
         ([-1.0, -1.0, -1.0], CORNER_BTF_L),