Ensure Emacs-style Ctrl-b/Ctrl-f work when terminals send bare control
chars.
- Map ^B (U+0002) to move left when no CONTROL modifier is reported.
- Map ^F (U+0006) to move right when no CONTROL modifier is reported.
- Preserve existing Ctrl-b/Ctrl-f and Alt-b/Alt-f behavior.
- Add unit test covering the fallback path.
Background: Ghostty (and some tmux/terminal configs) can emit bare
control characters for Ctrl-b/Ctrl-f. Previously these could be treated
as literal input; with this change both styles behave identically.
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