fix(sw): square the multi step header process ends

- SWProcessHeader appearance="multi": the process base and both end
  covers meet the file name and the window area with right angles
  (border-radius 0, multi block only). default keeps the Strana top
  corners 6 / covers 5; step tabs, arrows, colors and sizes unchanged
- DESIGN_RULES §14 and Step Header spec §9.2 record the multi-only rule
- process-header-states.check.mjs: default 6 / 5 kept, multi 0 (17/17);
  build:sw and check:ai-docs pass, Storybook zoom shows square multi ends

packages/sw/src/theme/sw-process-header.css

@@ -529,6 +529,10 @@
   --hm-sw-process-shape-start: 50px;
   --hm-sw-process-shape-end: 48px;
 }
+/* Square ends (2026-11-05 user decision, `multi` only): the base and the end covers meet the file name and the window
+   area with right angles. `default` keeps the Strana top corners 6 (cover 5); the step tabs keep their own shapes. */
+.hm-sw-process-bar[data-appearance="multi"]::before,
+.hm-sw-process-bar[data-appearance="multi"] > .hm-sw-process-bar__rest { border-radius: 0; }
 .hm-sw-process-bar[data-appearance="multi"] .hm-sw-process-bar__group {
   flex-direction: column;
   align-items: flex-start;