refactor(ui): validation as errors on attempt, help text behind the ? (#1561)

The founder flagged the app as bloated with standing instructional text.

Ny verifikation: the what's-missing lines (Ange en beskrivning, Minst
två rader...) rendered from the first frame because their only gate was
form validity, which an empty form fails: instructions dressed as
validation. The submit buttons now stay enabled and an attempt on an
incomplete form is what surfaces the lines, in destructive red, per the
error-on-submit idiom. The Enter-to-advance flow keeps the old
completeness predicate so navigation is untouched.

Matcha mot befintlig verifikation: the two-sentence explainer moved
behind a ? (HelpPopover, convention 7), the N:1 note tightened, the
Visa även matchade switch became a quiet link (switches are settings
idiom), and Stark träff, the normal auto-selected case, renders as
muted text instead of a chip (chips mark exceptions, convention 5).

Deleted always-visible paraphrase lines and their orphaned keys:
items_card_description, picker_description, references_subtitle,
sort_stack_hint, dimensions hints, document_help, and the dead
fill_balance_hint key that had no render site at all.

Co-authored-by: Jakob Wennberg <311770904+jakobwennberg-oss@users.noreply.github.com>
Co-authored-by: Claude Fable 5 <noreply@anthropic.com>

app/(dashboard)/bookkeeping/[id]/page.tsx

@@ -936,7 +936,6 @@ export default function JournalEntryDetailPage({ params }: { params: Promise<{ i
             <div className="mb-4 space-y-2">
               <div>
                 <h4 className="text-sm font-medium">{t('references_title')}</h4>
-                <p className="text-xs text-muted-foreground">{t('references_subtitle')}</p>
               </div>
               <ul className="space-y-1">
                 {references.map((ref) => (