Formula bar improvements

Several quality-of-life improvements to the formula bar and formula editing experience.

Collapsible formula help panel

The formula documentation panel (shown when typing a function like =SUM() can now be collapsed into a compact one-line signature hint. Click the ▾ toggle in the panel header to shrink it out of the way — the active parameter stays highlighted in the signature so you don't lose context. Click ▸ to expand it again, or × to close it entirely.

Color highlights in the formula bar

Cell references in the formula bar now show colored background highlights matching the colored outlines on the grid. When you type =SUM(A1:B5, D1:D10), each range token is tinted with its corresponding color — the same visual language as the selection boxes on the sheet.

Smarter autocomplete

The function autocomplete no longer fires when the cursor is inside a cell reference. Typing =SUM(E12) and navigating within E12 previously showed a list of functions starting with "E" — that spurious popup is now suppressed.