feat: Add email settings management and templates functionality

- Implemented email settings configuration in the admin panel, allowing for SMTP settings and notification preferences.
- Created a new template for email settings with fields for SMTP host, port, username, password, sender address, and recipients.
- Added JavaScript functionality to handle loading, saving, and validating email settings.
- Introduced email templates management, enabling the listing, editing, and saving of email templates.
- Updated navigation to include links to email settings and templates.
- Added tests for email settings and templates to ensure proper functionality and validation.

server/services/email_templates.py

@@ -0,0 +1,86 @@
+"""Email template management helpers."""
+from __future__ import annotations
+
+from dataclasses import dataclass
+from typing import Dict, List
+
+from ..database import get_app_settings, update_app_setting
+from .. import settings
+
+
+@dataclass(frozen=True)
+class EmailTemplateDefinition:
+    """Definition metadata describing an editable email template."""
+
+    id: str
+    setting_key: str
+    name: str
+    description: str
+    default_content: str
+
+
+EMAIL_TEMPLATE_DEFINITIONS: Dict[str, EmailTemplateDefinition] = {
+    "newsletter_confirmation": EmailTemplateDefinition(
+        id="newsletter_confirmation",
+        setting_key="newsletter_confirmation_template",
+        name="Newsletter Confirmation",
+        description="HTML email sent to subscribers immediately after they confirm their newsletter signup.",
+        default_content=getattr(
+            settings, "NEWSLETTER_CONFIRMATION_TEMPLATE", "").strip(),
+    ),
+}
+
+
+def list_templates() -> List[dict]:
+    """Return a list of metadata describing available email templates."""
+    return [
+        {
+            "id": definition.id,
+            "name": definition.name,
+            "description": definition.description,
+        }
+        for definition in EMAIL_TEMPLATE_DEFINITIONS.values()
+    ]
+
+
+def _load_stored_templates() -> dict:
+    """Return stored template values keyed by their setting key."""
+    return get_app_settings()
+
+
+def load_template(template_id: str) -> dict:
+    """Return template metadata and content for the requested template."""
+    if template_id not in EMAIL_TEMPLATE_DEFINITIONS:
+        raise KeyError(template_id)
+
+    definition = EMAIL_TEMPLATE_DEFINITIONS[template_id]
+    stored = _load_stored_templates()
+    content = stored.get(definition.setting_key, definition.default_content)
+
+    return {
+        "id": definition.id,
+        "name": definition.name,
+        "description": definition.description,
+        "content": content,
+    }
+
+
+def persist_template(template_id: str, content: str) -> dict:
+    """Persist template content and return the updated template payload."""
+    if template_id not in EMAIL_TEMPLATE_DEFINITIONS:
+        raise KeyError(template_id)
+
+    definition = EMAIL_TEMPLATE_DEFINITIONS[template_id]
+    content = (content or "").strip()
+    update_app_setting(definition.setting_key, content)
+    return load_template(template_id)
+
+
+def get_template_content(template_id: str) -> str:
+    """Return just the template body, falling back to defaults when unset."""
+    if template_id not in EMAIL_TEMPLATE_DEFINITIONS:
+        raise KeyError(template_id)
+
+    definition = EMAIL_TEMPLATE_DEFINITIONS[template_id]
+    stored = _load_stored_templates()
+    return stored.get(definition.setting_key, definition.default_content)