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/widget/QuickSettings.tsx

@@ -176,6 +176,14 @@ function Toggles() {
       </box>
       <box class="qs-tiles" spacing={8} homogeneous>
         <Tile icon={""} label="Pick Color" onClicked={() => { closePanel(); sh("hyprpicker -a") }} />
+        <Tile
+          icon={""}
+          label="Theme"
+          onClicked={() => {
+            closePanel()
+            sh("blob_theme")
+          }}
+        />
       </box>
     </box>
   )