Add theme system: local themes, picker, static/dynamic mode

- blob_theme: apply local or shared themes, --dynamic recolors from
  the current wallpaper without changing it, --print saves the active
  theme's colors.toml (e.g. for a dynamic palette worth keeping)
- themes/: drop-in colors.toml files that install.sh syncs into
  Omarchy's theme dir, alongside any already-installed themes
- ThemePicker widget, walker menu, and Quick Settings tile mirroring
  the existing wallpaper picker, with color-swatch previews
- blob_wallpaper no longer forces dynamic mode on every wallpaper
  change; it only recolors if you're already in dynamic mode
- install.sh: fix a new-directory mkdir bug in backup_and_copy, and
  stop backing up wallpapers/themes (.bak dirs were showing up as
  fake entries in the picker) since both are pure git mirrors

Claude-Session: https://claude.ai/code/session_011kf23kB9NsaczSYazZsWs6

ags/app.ts

@@ -4,6 +4,7 @@ import Media from "./widget/Media"
 import NotificationCenter from "./widget/Notifications"
 import QuickSettings from "./widget/QuickSettings"
 import SysMonitor from "./widget/SysMonitor"
+import ThemePicker from "./widget/ThemePicker"
 import WallPicker from "./widget/WallPicker"
 
 const SHOW_DESKTOP_MEDIA = false
@@ -25,6 +26,7 @@ app.start({
     start("notification-center", NotificationCenter)
     start("quick-settings", QuickSettings)
     start("sys-monitor", SysMonitor)
+    start("theme-picker", ThemePicker)
     start("wall-picker", WallPicker)
   },
 })