The B1 decision tree exposed a "Skip this step" affordance on
intermediate non-leaf nodes that broke the narrowing model — clicking
it left the tree in a half-narrowed state with no clear UX intent.
Drop the button entirely; users who don't know an answer should pick
"Anderes / Sonstiges" or switch to B2 (filter mode).
The step-back button (and its sibling .fristen-b1-loosen-link in the
empty-result state) rendered with `color: var(--color-accent)` over a
transparent background — lime green text on cream is unreadable. Move
both to a secondary-button shape: hairline border, muted text, accent
on focus-visible. Both light and dark themes verified.
Touched:
- frontend/src/client/fristenrechner.ts: drop skip TSX + handler
- frontend/src/client/i18n.ts: drop "deadlines.pathway.b.tree.skip"
- frontend/src/i18n-keys.ts: drop the codegen key
- frontend/src/styles/global.css: split off .fristen-b1-skip selector
and replace the lime-text rule with a bordered secondary style
using --color-text-muted / --color-border (themed both ways)
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