feat: add Products context with provider integration (Phase 1)

Implement the schema foundation for syncing products from POD providers
like Printify. This includes encrypted credential storage, product/variant
schemas, and an Oban worker for background sync.

New modules:
- Vault: AES-256-GCM encryption for API keys
- Products context: CRUD and sync operations for products
- Provider behaviour: abstraction for POD provider implementations
- ProductSyncWorker: Oban job for async product sync

Schemas: ProviderConnection, Product, ProductImage, ProductVariant

Also reorganizes Printify client to lib/simpleshop_theme/clients/ and
mockup generator to lib/simpleshop_theme/mockups/ for better structure.

134 tests added covering all new functionality.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

lib/simpleshop_theme/clients/printify.ex

@@ -0,0 +1,209 @@
+defmodule SimpleshopTheme.Clients.Printify do
+  @moduledoc """
+  HTTP client for the Printify API.
+
+  Handles authentication and provides low-level API access.
+  Requires PRINTIFY_API_TOKEN environment variable to be set.
+  """
+
+  @base_url "https://api.printify.com/v1"
+
+  @doc """
+  Get the API token.
+
+  Checks process dictionary first (for provider connections with stored credentials),
+  then falls back to environment variable (for development/mockup generation).
+  """
+  def api_token do
+    Process.get(:printify_api_key) ||
+      System.get_env("PRINTIFY_API_TOKEN") ||
+      raise "PRINTIFY_API_TOKEN environment variable is not set"
+  end
+
+  @doc """
+  Make a GET request to the Printify API.
+  """
+  def get(path, _opts \\ []) do
+    url = @base_url <> path
+
+    case Req.get(url, headers: auth_headers(), receive_timeout: 30_000) do
+      {:ok, %Req.Response{status: status, body: body}} when status in 200..299 ->
+        {:ok, body}
+
+      {:ok, %Req.Response{status: status, body: body}} ->
+        {:error, {status, body}}
+
+      {:error, reason} ->
+        {:error, reason}
+    end
+  end
+
+  @doc """
+  Make a POST request to the Printify API.
+  """
+  def post(path, body, _opts \\ []) do
+    url = @base_url <> path
+
+    case Req.post(url, json: body, headers: auth_headers(), receive_timeout: 60_000) do
+      {:ok, %Req.Response{status: status, body: body}} when status in 200..299 ->
+        {:ok, body}
+
+      {:ok, %Req.Response{status: status, body: body}} ->
+        {:error, {status, body}}
+
+      {:error, reason} ->
+        {:error, reason}
+    end
+  end
+
+  @doc """
+  Make a DELETE request to the Printify API.
+  """
+  def delete(path, _opts \\ []) do
+    url = @base_url <> path
+
+    case Req.delete(url, headers: auth_headers(), receive_timeout: 30_000) do
+      {:ok, %Req.Response{status: status, body: body}} when status in 200..299 ->
+        {:ok, body}
+
+      {:ok, %Req.Response{status: status}} when status == 204 ->
+        {:ok, nil}
+
+      {:ok, %Req.Response{status: status, body: body}} ->
+        {:error, {status, body}}
+
+      {:error, reason} ->
+        {:error, reason}
+    end
+  end
+
+  @doc """
+  Get all shops for the authenticated account.
+  """
+  def get_shops do
+    get("/shops.json")
+  end
+
+  @doc """
+  Get the first shop ID for the account.
+  """
+  def get_shop_id do
+    case get_shops() do
+      {:ok, shops} when is_list(shops) and length(shops) > 0 ->
+        {:ok, hd(shops)["id"]}
+
+      {:ok, []} ->
+        {:error, :no_shops}
+
+      error ->
+        error
+    end
+  end
+
+  @doc """
+  Get all blueprints (product types) from the catalog.
+  """
+  def get_blueprints do
+    get("/catalog/blueprints.json")
+  end
+
+  @doc """
+  Get print providers for a specific blueprint.
+  """
+  def get_print_providers(blueprint_id) do
+    get("/catalog/blueprints/#{blueprint_id}/print_providers.json")
+  end
+
+  @doc """
+  Get variants for a specific blueprint and print provider.
+  """
+  def get_variants(blueprint_id, print_provider_id) do
+    get("/catalog/blueprints/#{blueprint_id}/print_providers/#{print_provider_id}/variants.json")
+  end
+
+  @doc """
+  Get shipping information for a blueprint/provider combination.
+  """
+  def get_shipping(blueprint_id, print_provider_id) do
+    get("/catalog/blueprints/#{blueprint_id}/print_providers/#{print_provider_id}/shipping.json")
+  end
+
+  @doc """
+  Upload an image to Printify via URL.
+  """
+  def upload_image(file_name, url) do
+    post("/uploads/images.json", %{
+      file_name: file_name,
+      url: url
+    })
+  end
+
+  @doc """
+  Create a product in a shop.
+  """
+  def create_product(shop_id, product_data) do
+    post("/shops/#{shop_id}/products.json", product_data)
+  end
+
+  @doc """
+  Get a product by ID.
+  """
+  def get_product(shop_id, product_id) do
+    get("/shops/#{shop_id}/products/#{product_id}.json")
+  end
+
+  @doc """
+  List all products in a shop.
+  """
+  def list_products(shop_id, opts \\ []) do
+    limit = Keyword.get(opts, :limit, 100)
+    page = Keyword.get(opts, :page, 1)
+    get("/shops/#{shop_id}/products.json?limit=#{limit}&page=#{page}")
+  end
+
+  @doc """
+  Delete a product from a shop.
+  """
+  def delete_product(shop_id, product_id) do
+    delete("/shops/#{shop_id}/products/#{product_id}.json")
+  end
+
+  @doc """
+  Create an order in a shop.
+  """
+  def create_order(shop_id, order_data) do
+    post("/shops/#{shop_id}/orders.json", order_data)
+  end
+
+  @doc """
+  Get an order by ID.
+  """
+  def get_order(shop_id, order_id) do
+    get("/shops/#{shop_id}/orders/#{order_id}.json")
+  end
+
+  @doc """
+  Download a file from a URL to a local path.
+  """
+  def download_file(url, output_path) do
+    case Req.get(url, into: File.stream!(output_path), receive_timeout: 60_000) do
+      {:ok, %Req.Response{status: status}} when status in 200..299 ->
+        {:ok, output_path}
+
+      {:ok, %Req.Response{status: status}} ->
+        File.rm(output_path)
+        {:error, {:http_error, status}}
+
+      {:error, reason} ->
+        File.rm(output_path)
+        {:error, reason}
+    end
+  end
+
+  defp auth_headers do
+    [
+      {"Authorization", "Bearer #{api_token()}"},
+      {"Content-Type", "application/json"}
+    ]
+  end
+end