Fix invisible cinema CTA buttons on What's On #1

Screenshot from 2026-09-11 shows the two main cinema CTA buttons on the What's On page as white-on-white: Cineworld Swindon and Vue Swindon primary buttons appear to have lost their intended background colour, while the secondary Club Vue ↗ button remains readable.

Likely cause to verify: primary CTA class/background variable not being applied or overridden in the current generated CSS. Do not patch only the rendered HTML if the rule belongs in shared code.

Tomorrow's fix should start from the canonical Markdown source, expected /whats-on/whats-on-page.md, plus SwindonOrgUK-GUI.md and shared code.md, then regenerate the HTML.

Acceptance checks:

• Cineworld primary CTA has visible text and intended coloured background.
• Vue primary CTA has visible text and intended coloured background.
• Club Vue ↗ remains readable as secondary action.
• hover/focus states retain sufficient contrast.
• desktop and mobile both work.
• if the root cause is a shared CTA component, fix it in code.md so other pages inherit the correction.
• add/retain the requirement in the page Markdown so a later AI regeneration cannot silently reintroduce white text on white background.

This is a good example of why page -page.md files are canonical build memory rather than optional notes.