Standard viewport, alt text on every image, a post heading, one stylesheet !19

Stacked on !18; retarget to main once that merges.

• #28 width=device-width, initial-scale=1 instead of initial-scale=0.4 plus the fake height=device-height; the portrait rules that compensated (* { font-size: 120% }, 200% widths, 60% form text) are gone or resized. Checked the index and about pages at phone width and desktop locally.
• #29 Listing thumbnails, comment avatars, user plates, folder thumbnails and description embeds carry alt. The post title is an h1 (styled to its old size).
• #30 The index page's inline stylesheet lives in skunky.css under .index.

One new test for the alt text on the Go-built images.

Closes #28 Closes #29 Closes #30