feat: add Settings and Media contexts with theme settings schema

- Create settings table for site-wide key-value configuration
- Create images table for BLOB storage of logo/header images
- Add Setting schema with JSON/string/integer/boolean support
- Add ThemeSettings embedded schema with all theme options
- Add Settings context with get/put/update operations
- Add Media context for image uploads and retrieval
- Add Image schema with SVG detection and storage
- Add 9 curated theme presets (gallery, studio, boutique, etc.)
- Add comprehensive tests for Settings and Media contexts
- Add seeds with default Studio preset
- All tests passing (29 tests, 0 failures)

priv/repo/migrations/20251230213057_create_settings.exs

@@ -0,0 +1,16 @@
+defmodule SimpleshopTheme.Repo.Migrations.CreateSettings do
+  use Ecto.Migration
+
+  def change do
+    create table(:settings, primary_key: false) do
+      add :id, :binary_id, primary_key: true
+      add :key, :string, null: false
+      add :value, :text, null: false
+      add :value_type, :string, null: false, default: "string"
+
+      timestamps(type: :utc_datetime)
+    end
+
+    create unique_index(:settings, [:key])
+  end
+end

priv/repo/migrations/20251230213058_create_images.exs

@@ -0,0 +1,21 @@
+defmodule SimpleshopTheme.Repo.Migrations.CreateImages do
+  use Ecto.Migration
+
+  def change do
+    create table(:images, primary_key: false) do
+      add :id, :binary_id, primary_key: true
+      add :image_type, :string, null: false
+      add :filename, :string, null: false
+      add :content_type, :string, null: false
+      add :file_size, :integer, null: false
+      add :data, :binary, null: false
+      add :is_svg, :boolean, default: false
+      add :svg_content, :text
+      add :thumbnail_data, :binary
+
+      timestamps(type: :utc_datetime)
+    end
+
+    create index(:images, [:image_type])
+  end
+end

priv/repo/seeds.exs

@@ -9,3 +9,12 @@
 #
 # We recommend using the bang functions (`insert!`, `update!`
 # and so on) as they will fail if something goes wrong.
+
+alias SimpleshopTheme.Settings
+
+# Set default theme settings (Studio preset)
+IO.puts("Setting up default theme settings...")
+
+{:ok, _theme} = Settings.apply_preset(:studio)
+
+IO.puts("✓ Default theme settings applied (Studio preset)")