refactor(webui): css quality overhaul with scoped styles, class selectors, design...

refactor(webui): css quality overhaul with scoped styles, class selectors, design tokens

- add scoped to all 12 Vue component style blocks
- move body/app global styles to index.html
- replace all 33 ID CSS selectors with class selectors
- add :deep() for parent-child table style propagation
- add spacing scale and typography tokens to all themes
- replace magic number percentages with spacing variables
- add :focus-visible styles for buttons and select
- replace hardcoded form widths with max-width constraints
- use gap for flex toolbar spacing
- remove dead CSS