Consistent by default or configurable mode switching

This issue is to track the suggestion that key binding for mode switching may be changed (https://github.com/anthropics/claude-code/issues/3368#issuecomment-3082026356). This is not a duplicate of https://github.com/anthropics/claude-code/issues/3368.

At the time of this writing, https://github.com/anthropics/claude-code/issues/3368#issuecomment-3079262659 shows approx 7:1 favor of using shift + tab on Windows for versions of node where it works and falling back to alt + m. Alternately, allowing the key to be configured would also likely satisfy these users.