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/extensions/general/InvoiceInboxWorkspace.tsx

@@ -1793,7 +1793,7 @@ export default function InvoiceInboxWorkspace(_props: WorkspaceComponentProps) {
             />
           )}
           {isDragging && (
-            <div className="absolute inset-0 bg-primary/5 border-2 border-dashed border-primary rounded-md m-4 flex items-center justify-center pointer-events-none">
+            <div className="absolute inset-0 bg-primary/5 border-2 border-dashed border-primary rounded-lg m-4 flex items-center justify-center pointer-events-none">
               <p className="text-sm font-medium text-primary">Släpp filen för att ladda upp</p>
             </div>
           )}
@@ -2235,7 +2235,7 @@ export function DocumentPreview({
     <div className="h-full w-full p-4 flex items-start justify-center overflow-hidden">
       {docMime?.startsWith('image/') ? (
         // Image: frame hugs the image, capped at the parent's visible box.
-        <div className="max-h-full max-w-3xl bg-background rounded-md border overflow-hidden flex">
+        <div className="max-h-full max-w-3xl bg-background rounded-lg border overflow-hidden flex">
           {/* eslint-disable-next-line @next/next/no-img-element */}
           <img
             src={docUrl}
@@ -2248,7 +2248,7 @@ export function DocumentPreview({
         // with no tokens = opaque origin, no scripts, no forms, no popups.
         // bg-white because mail HTML assumes a white canvas and would render
         // transparent (unreadable in dark mode) otherwise.
-        <div className="h-full w-full max-w-3xl bg-background rounded-md border overflow-hidden">
+        <div className="h-full w-full max-w-3xl bg-background rounded-lg border overflow-hidden">
           <iframe
             src={docUrl}
             sandbox=""
@@ -2258,7 +2258,7 @@ export function DocumentPreview({
         </div>
       ) : (
         // PDF: iframe needs explicit height, frame fills the available pane.
-        <div className="h-full w-full max-w-3xl bg-background rounded-md border overflow-hidden">
+        <div className="h-full w-full max-w-3xl bg-background rounded-lg border overflow-hidden">
           <iframe src={docUrl} className="w-full h-full border-0" title="Underlag" />
         </div>
       )}