fix(tui): reopen autocomplete after backspace deletes space

[Raviguntakala]

Problem

When typing / or @, autocomplete shows suggestions.
If you press space by mistake, the dropdown closes.
When you press backspace to remove the space, autocomplete does not come back, even though the text is valid again.

Steps to Reproduce

1. Type /something → autocomplete appears
2. Press space → autocomplete closes
3. Press backspace → autocomplete does not reopen

Fix

Updated the onInput logic to reopen autocomplete when the cursor is back in a valid position.

• For /
  Autocomplete reopens when the text starts with / and there is no space before the cursor

• For @
  Finds the closest @ before the cursor and reopens autocomplete if there is no space between @ and the cursor

Testing

• /something → space → backspace → autocomplete reopens
• @agent → space → backspace → autocomplete reopens
• Normal behavior is unchanged
• Text like test/path does not trigger / autocomplete

Screen.Recording.2025-12-23.at.6.31.46.PM.mov

Screen.Recording.2025-12-23.at.6.33.38.PM.mov