Share card and homepage links #69

Parent

#61

What to build

Make links to thirdshift.app look good when they're shared, and point the crate at the site.

• Card image: an Open Graph and Twitter card image of the press line (a static raster, e.g. 1200×630), in the site's look.
• Meta tags: og: and twitter: tags on both the home page and /prompts/ (if it exists when this lands; otherwise just the home page), with absolute URLs on https://thirdshift.app.
• Manifest: homepage = "https://thirdshift.app" in the package manifest. The README keeps its GitHub install command.

Acceptance criteria

• The card image exists at the recommended size and shows the press line.
• The home page has complete Open Graph and Twitter card tags with absolute URLs.
• The manifest's homepage is https://thirdshift.app, and the packaging test still passes.
• The README's install section is unchanged.

Blocked by

• Press line, static: the full How a Run works diagram in HTML and SVG #64