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 <noreply@anthropic.com>
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