rework email settings for true progressive enhancement

Render all adapter field sections in the form with CSS :has(:checked)
controlling visibility. Selecting a provider instantly shows its config
fields — no JS, no page reload, no server round-trip needed.

- Render all 6 adapter configs with data-adapter attribute
- CSS :has(:checked) show/hide rules per adapter in admin stylesheet
- Namespace field names per adapter (email[brevo][api_key] etc)
- Drop 4 transactional-only providers (Resend, Postmark, Mailgun, MailPace)
- Remove noscript "Switch provider" button and controller redirect workaround
- Remove configured_adapter hidden input tracking
- Hide JS-only test email button for no-JS users via noscript style
- LiveView progressively enhances with async save and test email

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

lib/berrypod/key_validation.ex

@@ -84,8 +84,6 @@ defmodule Berrypod.KeyValidation do
   @known_prefixes [
     {"SG.", "SendGrid"},
     {"xkeysib-", "Brevo"},
-    {"re_", "Resend"},
-    {"key-", "Mailgun"},
     {"mlsn.", "MailerSend"}
   ]
 
@@ -98,56 +96,6 @@ defmodule Berrypod.KeyValidation do
     end
   end
 
-  # Postmark: UUID format
-  defp validate_email_format(key, "postmark", "api_key") do
-    uuid_pattern = ~r/^[0-9a-f]{8}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{4}-[0-9a-f]{12}$/i
-
-    cond do
-      Regex.match?(uuid_pattern, key) ->
-        {:ok, key}
-
-      wrong = wrong_provider_hint(key, "postmark") ->
-        {:error, wrong}
-
-      true ->
-        {:error,
-         "Postmark server tokens are UUIDs (like abc12345-abcd-1234-abcd-123456789abc). Make sure you copy the server token, not the account ID"}
-    end
-  end
-
-  # Resend: re_ prefix
-  defp validate_email_format(key, "resend", "api_key") do
-    cond do
-      String.starts_with?(key, "re_") ->
-        {:ok, key}
-
-      wrong = wrong_provider_hint(key, "resend") ->
-        {:error, wrong}
-
-      true ->
-        {:error,
-         "Resend API keys start with re_ — find yours in your Resend dashboard under API Keys"}
-    end
-  end
-
-  # Mailgun: key- prefix (classic) or long RBAC keys
-  defp validate_email_format(key, "mailgun", "api_key") do
-    cond do
-      String.starts_with?(key, "key-") ->
-        {:ok, key}
-
-      String.length(key) >= 20 ->
-        {:ok, key}
-
-      wrong = wrong_provider_hint(key, "mailgun") ->
-        {:error, wrong}
-
-      true ->
-        {:error,
-         "Mailgun API keys usually start with key- — find yours in Settings → API Security"}
-    end
-  end
-
   # Brevo: xkeysib- prefix
   defp validate_email_format(key, "brevo", "api_key") do
     cond do
@@ -210,21 +158,6 @@ defmodule Berrypod.KeyValidation do
     end
   end
 
-  # MailPace: server token, no known prefix
-  defp validate_email_format(key, "mailpace", "api_key") do
-    cond do
-      String.length(key) >= 10 ->
-        {:ok, key}
-
-      wrong = wrong_provider_hint(key, "mailpace") ->
-        {:error, wrong}
-
-      true ->
-        {:error,
-         "This looks too short — find your server API token under your domain settings in MailPace"}
-    end
-  end
-
   # Non-api_key fields (domain, relay, base_url, etc.), basic checks
   defp validate_email_format(key, _adapter_key, _field_key) do
     if String.length(key) < 3 do

lib/berrypod/mailer/adapters.ex

@@ -69,64 +69,6 @@ defmodule Berrypod.Mailer.Adapters do
         %Field{key: "api_key", label: "API key", type: :secret, required: true}
       ]
     },
-    # ── Transactional only ──
-    %Adapter{
-      key: "resend",
-      name: "Resend",
-      module: Swoosh.Adapters.Resend,
-      description: "Developer-friendly API, simple setup.",
-      tags: ["Transactional", "US"],
-      category: :transactional,
-      free_tier: "3,000 emails/month free",
-      setup_hint: "Paste one API key",
-      url: "https://resend.com",
-      fields: [
-        %Field{key: "api_key", label: "API key", type: :secret, required: true}
-      ]
-    },
-    %Adapter{
-      key: "postmark",
-      name: "Postmark",
-      module: Swoosh.Adapters.Postmark,
-      description: "Excellent deliverability tracking.",
-      tags: ["Transactional", "US"],
-      category: :transactional,
-      free_tier: "100 emails/month free",
-      setup_hint: "Paste one API key",
-      url: "https://postmarkapp.com",
-      fields: [
-        %Field{key: "api_key", label: "API key", type: :secret, required: true}
-      ]
-    },
-    %Adapter{
-      key: "mailgun",
-      name: "Mailgun",
-      module: Swoosh.Adapters.Mailgun,
-      description: "EU region option available.",
-      tags: ["Transactional", "EU option", "Sweden"],
-      category: :transactional,
-      free_tier: "100 emails/day trial",
-      setup_hint: "API key + domain name",
-      url: "https://www.mailgun.com",
-      fields: [
-        %Field{key: "api_key", label: "API key", type: :secret, required: true},
-        %Field{key: "domain", label: "Domain", type: :string, required: true}
-      ]
-    },
-    %Adapter{
-      key: "mailpace",
-      name: "MailPace",
-      module: Swoosh.Adapters.MailPace,
-      description: "Privacy-focused, simple API.",
-      tags: ["Transactional", "UK"],
-      category: :transactional,
-      free_tier: "3,000 emails/month free",
-      setup_hint: "Paste one API key",
-      url: "https://mailpace.com",
-      fields: [
-        %Field{key: "api_key", label: "API key", type: :secret, required: true}
-      ]
-    },
     # ── Advanced ──
     %Adapter{
       key: "smtp",