Update branding

Update the Ferese symbols, appearance-specific wallpapers, and rounded wallpaper and theme previews. Bundle Figtree and add the Ferese name to the website header.

Verified configuration, theme, Settings, wallpaper and installer tests, both UI renderers, the static site build, and browser layouts.

docs/configuration.md

@@ -249,7 +249,7 @@ prevent popup cleanup.
 
 Settings → Appearance offers six paired themes: **Ferese Blue** (default),
 **Catppuccin**, **Gruvbox**, **Rosé Pine**, **Tokyo Night**, and **Everforest**.
-Ferese Blue uses the logo accent, `#3D7BE6`, and has light and dark variants.
+Ferese Blue uses the default accent, `#3D7BE6`, and has light and dark variants.
 Choose Light, Dark, or Auto in Settings or Control Center. Auto follows local
 07:00 and 19:00 boundaries unless you change its schedule.
 
@@ -278,13 +278,34 @@ one appearance.
 | `appearance.inactive-dim.amount` | number 0–1 | `0.15` | Darkening strength |
 | `appearance.inactive-dim.duration-ms` | number ≥ 0 | `150` | Dimming transition; 0 snaps |
 | `theme.typography.font-family` | string | `"Inter"` | Shell, Settings and overview font |
-| `theme.background.path` | string | bundled Ferese wallpaper | Wallpaper image path; an existing selection overrides the default |
+| `theme.background.path` | string | matching light/dark wallpaper | Shared wallpaper; an explicit path overrides both bundled defaults |
+| `theme.light.background.path`, `theme.dark.background.path` | string | shared path, or matching default | Wallpaper for one appearance; overrides the shared path |
 | `theme.background.mode` | `"fill"`, `"fit"` | `"fill"` | Crop or letterbox |
+| `theme.light.background.mode`, `theme.dark.background.mode` | `"fill"`, `"fit"` | shared placement | Image placement for one appearance |
 | `theme.material.style` | `"solid"`, `"translucent"` | `"solid"` | Shell background material |
 | `theme.material.opacity` | number 0–1 | `0.78` | Shared shell background opacity for bars, menus, popovers, notifications and themed dialogs. Text/icons stay opaque; 0 hides the material. Solid mode is always opaque |
 | `theme.material.tint-strength` | number 0–1 | Dark `0.5`, light `1` | Color strength over the blurred backdrop |
 | `theme.material.blur-radius` | number ≥ 0 | `12` | Translucent backdrop blur, capped at 32; 0 disables |
 
+Settings → Wallpaper shows the current image and both bundled defaults. Use
+**Apply to** to change both modes or just one. **Match appearance** restores the
+bundled light and dark pair. Custom images can also be selected separately in KDL:
+
+```kdl
+theme {
+    light {
+        background { path "~/Pictures/day.png"; }
+    }
+    dark {
+        background { path "~/Pictures/night.jpg"; }
+    }
+}
+```
+
+The wallpaper follows manual light/dark changes and automatic appearance changes.
+A shared `theme.background.path` applies to both modes unless a per-mode path
+is set.
+
 | `theme.colors` key | Default | Meaning |
 | --- | --- | --- |
 | `surface-base` | `"#111821"` | Material/card base color |