Release v0.51.250 — Release HR (stage-q22) (#3526)

## Release v0.51.250 — Release HR (stage-q22)

UX-approved (dark + light-fallback screenshots).

### Added
| PR | Author | Feature |
|----|--------|---------|
| #3328 | @heagandev | **Zeus appearance skin** — OLED-near-black dark surfaces that keep the default **gold accent** (a high-contrast "gold on black" look no existing skin offered). Selectable from Settings → Appearance or `/theme skin zeus`. Dark-focused; falls back to the default light palette in light mode. |

### Notes
- The PR was 2 days / ~19 releases stale and CONFLICTING; re-applied surgically onto current master (CSS palette + `zeus` registered at all 5 sites: config allowlist, boot.js swatch, index.html boot-map, i18n `cmd_theme` ×12 locales, picker) + THEMES.md doc row. The PR's own `test_zeus_skin.py` (6 tests) passes against the re-applied version.
- Fully scoped + additive: Codex verified every new CSS rule is under `:root.dark[data-skin="zeus"]` — no bleed into the default appearance or other skins.

### Gate
- Full pytest suite: **7563 passed, 0 failed**
- ESLint: CLEAN · ruff: CLEAN · browser-smoke: CLEAN · vision-verified dark (OLED+gold) + light (clean fallback)
- Codex (regression): **SAFE TO SHIP**

Co-authored-by: heagandev <heagandev@users.noreply.github.com>

THEMES.md

@@ -21,7 +21,7 @@ Preview is instant — the UI updates as you click.
 **Slash command:** Type `/theme <name>` in the composer. The command accepts
 both theme names (`system`, `dark`, `light`) and skin names (`default`, `ares`,
 `mono`, `slate`, `poseidon`, `sisyphus`, `charizard`, `sienna`,
-`catppuccin`, `nous`, `geist-contrast`). It updates the matching axis and leaves the other one
+`catppuccin`, `nous`, `geist-contrast`, `zeus`). It updates the matching axis and leaves the other one
 alone.
 
 **Persistence:** Both choices are stored in `localStorage` for flicker-free
@@ -58,6 +58,7 @@ absent for light. System mode tracks the OS preference at runtime.
 | **Catppuccin** | Catppuccin Latte/Mocha palette with Mauve accent. |
 | **Nous** | Steel-blue accent with dashed technical surfaces. |
 | **Geist Contrast** (`geist-contrast`) | Geist-inspired monochrome surfaces with a restrained dark-mode `#FFF175` accent. |
+| **Zeus** | OLED-near-black dark surfaces that keep the default gold accent. Dark-focused; falls back to the default light palette in light mode. |
 
 Each skin defines paired light + dark variants so it reads cleanly on either
 theme. The skin is applied as `data-skin="<name>"` on `<html>` (the default