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>

components/invoices/InvoiceEditor.tsx

@@ -1565,7 +1565,6 @@ export default function InvoiceEditor(props: InvoiceEditorProps = { mode: 'creat
             <Card>
               <CardHeader>
                 <CardTitle>{t('items_card_title')}</CardTitle>
-              <CardDescription>{t('items_card_description')}</CardDescription>
             </CardHeader>
             <CardContent>
               <div className="space-y-4">
@@ -2386,9 +2385,6 @@ export default function InvoiceEditor(props: InvoiceEditorProps = { mode: 'creat
                           onChange={setDefaultDimension}
                           inputClassName="h-9"
                         />
-                        <p className="text-xs text-muted-foreground">
-                          {t('dimensions_default_hint')}
-                        </p>
                       </div>
                     </>
                   )}