Fix icon alignment and hit targets per macOS HIG

[datlechin]

Summary

• Add .frame(width: 24, height: 24) to all icon-only borderless/plain buttons for macOS HIG minimum hit targets (was ~14pt, now 24pt)
• Replace hardcoded .font(.system(size: N)) on SF Symbols with semantic styles (.font(.largeTitle), .font(.title), .imageScale()) or let the system handle sizing via .controlSize(.small)
• Replace hardcoded Color.red/.yellow/.orange with system semantic colors (Color(nsColor: .systemRed), etc.)
• Add .contentShape(Circle()) to onboarding pagination dots for proper tap targets
• Remove unnecessary manual font sizing from toolbar sub-components (SafeModeBadgeView, ConnectionStatusView) — let the native toolbar system handle icon sizing

Closes #629

Test plan

• Open a table tab, toggle filters — verify +/- buttons are easy to click and visually aligned
• Check pagination chevrons and settings gear in status bar
• Check safe mode badge in toolbar
• Check SQL preview sheet close button
• Check query editor toolbar (clear, format buttons)
• Check EXPLAIN result font size buttons
• Check DDL view font size buttons in table structure
• Check history panel clear button
• Check database switcher refresh/create buttons
• Check AI settings provider list +/-/edit buttons
• Check favorites sidebar bottom toolbar buttons
• Check inline error banner copy/dismiss buttons
• Check onboarding pagination dots are tappable