Modern in the logo's colours, and the logo in the page's mode (#63)

Modern's palette was sampled from the 2004 iPodderX icon: a neutral navy,
its screen blue and amber EQ bars. It now takes the new logo's colours,
the dark half from logo-dark.svg (navy ground, #8fc2ea scale, #ff6a1a
needle) and the light half from logo.svg (sky ground, #2f6aa0 scale, the
needle taken down to #c43e00 so white on it clears AA). The pending amber
and the error red moved apart from the needle's orange, and the sign-in
page's copy of the palette follows.

The pages always showed logo.svg, the light variant, even in a dark
theme; logo-dark.svg was never served. It is now, and the app and admin
pages show whichever matches data-mode, dark until the script says light,
as the palette is. The sign-in page, which has no account's theme, picks
by the system's with <picture>.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

src/web.rs

@@ -68,6 +68,7 @@ pub fn router(state: WebState) -> Router {
         .route("/api/login", post(login))
         .route("/icon.png", get(icon))
         .route("/logo.svg", get(logo))
+        .route("/logo-dark.svg", get(logo_dark))
         .route("/favicon.ico", get(favicon))
         .route("/favicon.png", get(favicon))
         .route("/apple-touch-icon.png", get(touch_icon))
@@ -562,6 +563,15 @@ async fn logo() -> impl IntoResponse {
     )
 }
 
+/// logo.svg recoloured for a dark page. The pages pick one or the other by their light or dark
+/// mode.
+async fn logo_dark() -> impl IntoResponse {
+    (
+        [(header::CONTENT_TYPE, "image/svg+xml"), (header::CACHE_CONTROL, "max-age=86400")],
+        include_str!("../web/logo-dark.svg"),
+    )
+}
+
 /// The 2004 icon. Nothing here shows it any more; it stays for whatever outside ipx links to it.
 async fn icon() -> impl IntoResponse {
     (