Add polished collapsible control groups across the app

Kromacut?s control panels are growing as more tools and settings are added. Sections/groups throughout the app should support collapsing and expanding so users can save space and focus on the controls they are actively using.

This should apply broadly to grouped UI sections, including 2D mode, 3D mode, print settings, auto-paint sections, and future tools.

Desired behavior:

• Control groups can be collapsed and expanded.
• Collapsed/expanded state is remembered during use.
• Collapsed/expanded state is persisted to localStorage so the app reopens with the user?s preferred layout.
• The UI should fall back gracefully if storage is unavailable.
• Collapsed groups should still make it clear what section they contain.
• Important warnings, active states, counts, or changed/dirty indicators should remain discoverable when collapsed.

Design/UX notes:

• The interaction should feel polished, compact, and smooth.
• The goal is to save vertical space without making the UI feel hidden or fiddly.
• Group headers should have clear labels and obvious expand/collapse affordances.
• The pattern should feel consistent across the app.
• If a standard reusable group component already exists, this should build on it.
• If not, this is a good opportunity to create a reusable collapsible group component for control sections.

Desired outcome:
Users can collapse sections they are not using, keep frequently used controls open, and have Kromacut remember that layout, making complex 2D and 3D workflows feel cleaner and less crowded.

Start by locating the existing grouped control sections across 2D mode, 3D mode, print settings, and auto-paint, then check whether a reusable group component or localStorage pattern already exists. Done means groups collapse and expand consistently, preserve their state during use and across reopening, handle unavailable storage gracefully, and keep labels, warnings, counts, and changed indicators discoverable.