Release v4.68.1

Part of #95 (acceptance 1).

Added

• A real-Chromium accessibility audit of every screen template the default blueprint ships (business, foundation, state, support, auth, status, nesting chain): axe-core WCAG 2.0/2.1/2.2 A and AA including colour contrast and target size, no horizontal overflow, and landmark structure (one main, no duplicate/nested landmarks, unique names, all content in a landmark, a level-one heading) - in every data state, at desktop/tablet/phone widths, in the light and dark theme (1,000+ browser specifications), against the registry of a host with the blueprint's dependencies (core, PrimeReact with a theme preset, the blueprint). It runs in the JavaScript Build workflow's existing browser step, so a regression fails the Scene CI.
• A control specification that breaks the page it just judged (pale text, a second main, content outside a landmark, two tiny adjacent buttons) and expects each finding, so a clean audit is never vacuous.
• Documentation in blueprints/template-set.md ("In a real browser").

Fixed

• The bare core:button was 21 pixels high (WCAG 2.2 target size): the shell now gives a button in the content area, in the application and the full-page shell, a 2rem minimum.
• Two search landmarks on one page (topbar and list) had no accessible names: foundation:globalSearch now names its form with its label.
• A grid item kept min-width: auto, so a widget holding a wide table pushed its track past the window: a phone scrolled sideways and, on a desktop, the dashboard's primary column overlapped its secondary one. Every item of a template slot now shrinks to its track and the table scrolls inside itself.
• PrimeReact's Lara tag severities (info, success, warn, danger) paint white on a mid-tone in the light scheme (2.3 to 3.8:1): the blueprint darkens them to meet WCAG AA, the dark scheme's values are unchanged.

Both were found by the rendered vector on the live Stage and a generated React application (Cratis/Stage verification blueprint-templates, separate PR), where PrimeReact is styled; regression specifications for both are here.