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

elephant/menus/blob_theme_selector.lua

@@ -0,0 +1,76 @@
+Name = "blobThemeSelector"
+NamePretty = "Blob's Theme Selector"
+Cache = false
+HideFromProviderlist = true
+SearchName = true
+
+local function ShellEscape(s)
+  return "'" .. s:gsub("'", "'\\''") .. "'"
+end
+
+function FormatName(slug)
+  local name = slug:gsub("-", " ")
+  name = name:gsub("%S+", function(word)
+    return word:sub(1, 1):upper() .. word:sub(2):lower()
+  end)
+  return name
+end
+
+function GetEntries()
+  local entries = {}
+  local home = os.getenv("HOME")
+  local omarchy_path = os.getenv("OMARCHY_PATH") or ""
+
+  entries[1] = {
+    Text = "Dynamic (from wallpaper)",
+    Value = "dynamic",
+    Actions = {
+      activate = "blob_theme --dynamic",
+    },
+  }
+
+  local dirs = {
+    home .. "/.config/omarchy/themes",
+    omarchy_path .. "/themes",
+  }
+
+  local seen = { ["blob-dynamic"] = true }
+
+  for _, themes_dir in ipairs(dirs) do
+    local handle = io.popen(
+      "find " .. ShellEscape(themes_dir) .. " -mindepth 1 -maxdepth 1 -type d 2>/dev/null | sort"
+    )
+    if handle then
+      for theme_dir in handle:lines() do
+        local slug = theme_dir:match("([^/]+)$")
+        if slug and not seen[slug] then
+          local colors_file = io.open(theme_dir .. "/colors.toml", "r")
+          if colors_file then
+            colors_file:close()
+            seen[slug] = true
+
+            local entry = {
+              Text = FormatName(slug),
+              Value = slug,
+              Actions = {
+                activate = "blob_theme " .. ShellEscape(slug),
+              },
+            }
+
+            local preview_file = io.open(theme_dir .. "/preview.png", "r")
+            if preview_file then
+              preview_file:close()
+              entry.Preview = theme_dir .. "/preview.png"
+              entry.PreviewType = "file"
+            end
+
+            table.insert(entries, entry)
+          end
+        end
+      end
+      handle:close()
+    end
+  end
+
+  return entries
+end