style(org): standardize all project pages on darksun theme with responsive images

style(org): standardize all project pages on darksun theme with responsive images

- Add shared style.css with responsive-img, project-img, schematic-img classes

- All 31 individual pages: use darksun theme, remove per-page TWBS Bootstrap headers

- All individual pages: suppress author footer, add consistent back-links

- All images: add responsive-img class for max-width 600px

- Fix 35mm film copying device: add missing imglnk macro that caused export abort

- Root index.org: link to style.css

- .gitignore: exclude .idea/ and *.FCStd1