refactor(design): lock the border-radius ladder, one radius per role (#1607)

Seven radii were in circulation (4/5/6/8/12/16px + pill) with no rule for
which went where; one toolbar row on /transactions mixed four shape
languages. This locks a 4-tier ladder (design.md convention 16):

- pill: interactive toolbar controls (buttons, chips, pickers, segmented
  controls, toolbar search, count nubs)
- rounded-xl (12px): overlay tier: page panel, dialogs, slide-overs
- rounded-lg (8px): cards, form fields, popover/menu content, boxes
- rounded-sm (4px): nested leaves (menu items, checkboxes, kbd/code nubs)

Changes:
- New SegmentedControl primitive (pill-in-pill tablist, h-8) replaces the
  hand-rolled bg-muted/70 tablist copied across 11 files
- New ToolbarSearch primitive (pill, h-8) adopted on 9 page toolbars;
  dialog/picker searches keep the rounded-lg Input
- dialog.tsx 8px -> 12px, matching SettingsModal/slide-over/CommandPalette
- ContextPicker chips at the shared h-8 toolbar height
- ~300 rounded-md / bare rounded call sites remapped by role; auth icon
  tiles and the mobile nav sheet come down from 16px to 12px
- rounded-md, bare rounded, rounded-2xl and rounded-[Npx] are dead
  vocabulary, enforced by a new off-ladder-radius check in check:guards

Verified: lint 0 errors, 14422 unit tests pass, check:guards green, tsc
clean on all changed files, sandbox screenshots of transactions/
bookkeeping/granskning toolbars and the Ny verifikation dialog.

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

components/inbox/TransactionMatchPicker.tsx

@@ -345,7 +345,7 @@ export default function TransactionMatchPicker({
         {/* Underlag reference: what we're matching against, so a currency or
             amount mismatch with a candidate is obvious at a glance. */}
         {(total != null || supplier) && (
-          <div className="rounded-md border bg-muted/30 px-3 py-2 text-xs flex items-center gap-x-3 gap-y-1 flex-wrap">
+          <div className="rounded-lg border bg-muted/30 px-3 py-2 text-xs flex items-center gap-x-3 gap-y-1 flex-wrap">
             <span className="text-muted-foreground shrink-0">Underlag</span>
             {supplier && <span className="font-medium truncate">{supplier}</span>}
             {total != null && (
@@ -420,7 +420,7 @@ export default function TransactionMatchPicker({
                   onClick={() => void handlePick(c.id)}
                   disabled={!!matchingId}
                   className={cn(
-                    'w-full text-left flex items-center gap-3 py-3 hover:bg-muted/50 transition-colors px-2 -mx-2 rounded',
+                    'w-full text-left flex items-center gap-3 py-3 hover:bg-muted/50 transition-colors px-2 -mx-2 rounded-sm',
                     matchingId && !isMatching && 'opacity-50',
                   )}
                 >