Clicking a gallery image now opens a dedicated viewer instead of dumping you on
the raw file.
- GET /b/<name>/view?f=<img> — full-viewport viewer (registered before the file
catch-all so /view wins; non-image f 307-redirects to the raw file, traversal
and missing f 404).
- Fit (downscale-only) / 1:1 (natural pixels, scroll-to-pan) toggle that only
appears when the image is larger than the viewport — when it already fits,
Fit ≡ 1:1 so the toggle is hidden. Re-evaluates on resize.
- Download button + ✕/Esc back to the gallery. Australis-themed, progressive
JS (degrades to fit-only, no-JS still shows the image + download + back).
- 5 new tests (34 total, all green); verified Fit/1:1/hidden-toggle states in a
real browser.