Refine Vim-style e motion whitespace handling

[Codex]

e motion should stop at the current word end or the next word end when starting on whitespace; current behavior can skip past trailing whitespace to EOF.

• Motion semantics: Rework moveWordEnd to respect initial character type, only skip whitespace when starting on it, and abort when no subsequent word exists.
• Cursor safety: Prevent cursor from advancing past the last valid character when only trailing whitespace remains.

Example:

// Before: cursor on trailing spaces at end of text -> jumps past EOF
// After: cursor on trailing spaces -> no movement; cursor in word -> moves to word end
moveWordEnd(activeElement);