feat: keep footer at bottom when search has no results

[anth0nycodes]

What changes are introduced?

When a search returns no loaders, the grid collapses to the short "empty" message and the page ends up shorter than the window. The footer then sits right under the content instead of at the bottom.

• body is now a vertical flex column that's at least as tall as the window (min-height: 100vh, or 100dvh where supported).
• main gets flex: 1 so it fills the leftover space and pushes the footer down.
• main also gets width: 100%, because a flex item otherwise shrinks to fit its content and would get narrower when the grid is empty.

The sticky topbar still works, since the flex column doesn't affect position: sticky.

Any screenshots?

before:

after: