[Dararaaaa]

[FEATURE REQUEST] Background: a gradient over the picture

Type

• Feature

What and why

The picture can now wear a gradient over it, as CSS's linear-gradient does: an angle, a start color and an end color, in Settings › Appearance › Background.

• background_gradient switches it (false by default).
• background_gradient_angle turns it: 0 draws upward, and degrees increase clockwise, 0 to 360 (180.0 by default, top to bottom).
• background_gradient_from and background_gradient_to are its colors, read by src/settings/color.rs: #rgb, #rrggbb, #rrggbbaa, rgb(...), rgba(...), transparent, black and white (#00000000 both by default).
• The colors are strings, so a settings file speaks CSS and an alpha keeps its exact value (#202030cc never lands in a float's noise).

The gradient paints over the picture, across the picture's box — the terminal's column or the whole window, as Picture scope says — at the background opacity. gpui draws two stops only, so two colors are all.

validate() refuses an angle outside 0 to 360 and a color that does not read: the row shows why under the field and the saved value stays.

How it was tested

• Rebased onto upstream/main (fdca49a, which already carries PR1 and PR2) as 18512c7; the wallpaper, PRD, AGENTS, acceptance and both feature docs were merged against the T163/T164 changes already on main.
• cargo build, cargo fmt --all -- --check clean, cargo clippy --all-targets -- -D warnings clean.
• cargo test --lib: 443 passed; the 8 failures are the suite's sandbox-bound shell and registry tests, as on main.
• New tests: settings::color (each hex form, rgb/rgba, what is not a color), settings::tests::a_gradient_keeps_its_angle_and_colors (defaults, an angle and colors read back, a bad color refused), and the wallpaper's gradient tests.
• On screen: with background_gradient: true, angle 180 and #202030cc to #00000000, the picture dims toward the bottom; with #ff0000cc the gradient tints it red at the top, so it paints over the picture.

Screenshots

Checklist

• Hand-written files stay at or under 500 lines; comments one line.
• scripts/check.sh: fmt, clippy and tests clean, the sandbox's 8 known failures aside.
• PRD.md, AGENTS.md and tasks/acceptance.md updated.