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/kpi/KPISettingsDialog.tsx

@@ -166,7 +166,7 @@ export function KPISettingsDialog({ preferences, onSave, saving }: KPISettingsDi
                       <p className="font-medium text-foreground/80 mb-0.5">
                         {t('settings_formula_label')}
                       </p>
-                      <p className="font-mono text-[11px] bg-muted/50 rounded px-2 py-1">
+                      <p className="font-mono text-[11px] bg-muted/50 rounded-sm px-2 py-1">
                         {t(`def_${def.id}_formula`)}
                       </p>
                     </div>
@@ -189,7 +189,7 @@ export function KPISettingsDialog({ preferences, onSave, saving }: KPISettingsDi
                             setAccountOverride(def.id, e.target.value)
                           }
                           placeholder={def.defaultAccounts.join(', ')}
-                          className="w-full rounded-md border border-input bg-background px-2.5 py-1.5 text-xs font-mono tabular-nums placeholder:text-muted-foreground/50"
+                          className="w-full rounded-lg border border-input bg-background px-2.5 py-1.5 text-xs font-mono tabular-nums placeholder:text-muted-foreground/50"
                         />
                         <p className="mt-1 text-[10px] text-muted-foreground/70">
                           {t('settings_account_hint', { example: def.defaultAccounts.slice(0, 3).join(', ') })}