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/dashboard/UserMenu.tsx

@@ -63,7 +63,7 @@ function CompanyMark({ name }: { name: string }) {
   return (
     <span
       aria-hidden="true"
-      className="flex h-4 w-4 flex-shrink-0 items-center justify-center rounded-[4px] bg-secondary text-[9px] font-semibold uppercase leading-none text-foreground"
+      className="flex h-4 w-4 flex-shrink-0 items-center justify-center rounded-sm bg-secondary text-[9px] font-semibold uppercase leading-none text-foreground"
     >
       {name.trim().charAt(0) || '?'}
     </span>
@@ -193,7 +193,7 @@ export default function UserMenu({
   )
 
   const menuRow =
-    'flex w-full items-center gap-2.5 rounded-md px-2.5 py-2 text-left text-[13px] ' +
+    'flex w-full items-center gap-2.5 rounded-sm px-2.5 py-2 text-left text-[13px] ' +
     'text-muted-foreground hover:text-foreground hover:bg-secondary/60 ' +
     'transition-colors duration-150 cursor-pointer'
 
@@ -293,7 +293,7 @@ export default function UserMenu({
                         role="option"
                         aria-selected={c.id === company?.id}
                         className={cn(
-                          'flex w-full items-center gap-2 rounded-md px-2.5 py-2 text-left text-[13px] leading-snug transition-colors',
+                          'flex w-full items-center gap-2 rounded-sm px-2.5 py-2 text-left text-[13px] leading-snug transition-colors',
                           c.id === company?.id
                             ? 'bg-secondary/60 text-foreground'
                             : 'text-muted-foreground hover:bg-secondary/60 hover:text-foreground',