docs(sw): align AI docs and comments with the 2026-10-21 implementation

Documentation and comment-only changes (no component logic, Props or design change):
- VIEWER.md / AI_GUIDE / AI_USAGE / catalog / patterns: the two SWViewerHeader versions
  (default, and minimize/close with SWHeaderWindowControls at the end of `trailing`);
  the earlier "never mix SWHeader parts" rule now names this approved exception.
- collapseBelow / iconOnlyBelow (types.ts JSDoc, VIEWER.md, AI_GUIDE): measured steps,
  the numbers only set the order, not pixel breakpoints. Viewer file open is the
  onDocumentOpen button (logoMenu is compatibility only).
- COMPONENT_CATALOG / DESIGN_RULES: recent files show at most 3 rows; preview caption is
  previewTitle or path + file name; body is the red no-preview sign on the brown panel;
  preview / renderPreview are accepted but not rendered (JSDoc updated to match).
- packages/sw/README.md and sw-header-usage.md: current Story list and counts (40, 14
  shown + 26 verification); 760px+ no-More condition; read-only Property Bar values as
  <output>.
- SWHeader.tsx comment: titles are kept (not hidden) from 760px up.
- AI_GUIDE synced into the package ai/ copies (npm run sync:ai-docs).

packages/sw/src/components/sw-viewer/types.ts

@@ -70,9 +70,15 @@ interface SWViewerHeaderItemBase {
   disabled?: boolean
   /** Removed from the header and from More. */
   hidden?: boolean
-  /** Header width (px) below which the item moves into the More dropdown. */
+  /**
+   * Moves into the More dropdown when the measured header row has no room left, after the icons-only step. Not a pixel
+   * breakpoint: the value only sets the order (higher first; same value, rightmost first).
+   */
   collapseBelow?: number
-  /** Header width (px) below which only the icon is shown (label kept as the accessible name). */
+  /**
+   * Shows only the icon (label kept as tooltip and accessible name) when the measured header row has no room left; all
+   * such items switch together, before any item moves into More. Needs `icon`. Not a pixel breakpoint: any value.
+   */
   iconOnlyBelow?: number
   /** Always icon only (e.g. the info button). Needs `icon`. */
   iconOnly?: boolean