feat: add MVC Razor admin UI for email templates

- GetAllEmailTemplatesQuery + handler (new GetAll use case)
- IEmailTemplateRepository.GetAllAsync + EF implementation
- AdminTemplatesController: Index, Create, Edit, Save, Delete
- EmailTemplateEditViewModel with IsNew/PageTitle helpers
- Views/_ViewStart, _ViewImports, Shared/_Layout (Bootstrap 5)
- Shared/_EditorLayout (chained layout for all edit screens)
- Views/AdminTemplates/Index (table with edit/delete actions)
- Views/AdminTemplates/Edit (card form, readonly composite key on edit)
- Program.cs: AddControllersWithViews, UseStaticFiles, MapDefaultControllerRoute

Ref: IT-634

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

HrynCo.NotificationService.Web/Views/AdminTemplates/Edit.cshtml

@@ -0,0 +1,71 @@
+@using HrynCo.NotificationService.Web.Controllers.Admin.ViewModels
+@model EmailTemplateEditViewModel
+@{
+    Layout = "~/Views/Shared/_EditorLayout.cshtml";
+    ViewData["Title"] = Model.PageTitle;
+    ViewData["EditorTitle"] = Model.PageTitle;
+}
+
+<form asp-action="Save" asp-controller="AdminTemplates" method="post">
+    @Html.AntiForgeryToken()
+    <input asp-for="Id" type="hidden" />
+    <input type="hidden" name="IsNew" value="@Model.IsNew" />
+
+    @if (!ViewData.ModelState.IsValid)
+    {
+        <div class="alert alert-danger mb-3">
+            @foreach (var error in ViewData.ModelState.Values.SelectMany(v => v.Errors))
+            {
+                <div>@error.ErrorMessage</div>
+            }
+        </div>
+    }
+
+    <div class="mb-3">
+        <label asp-for="ServiceName" class="form-label fw-semibold">Service Name</label>
+        <input asp-for="ServiceName" class="form-control" readonly="@(!Model.IsNew)" />
+        <span asp-validation-for="ServiceName" class="text-danger small"></span>
+    </div>
+
+    <div class="mb-3">
+        <label asp-for="Key" class="form-label fw-semibold">Key</label>
+        <input asp-for="Key" class="form-control" readonly="@(!Model.IsNew)" />
+        <span asp-validation-for="Key" class="text-danger small"></span>
+    </div>
+
+    <div class="mb-3">
+        <label asp-for="LanguageCode" class="form-label fw-semibold">Language Code</label>
+        <input asp-for="LanguageCode" class="form-control" readonly="@(!Model.IsNew)" />
+        <span asp-validation-for="LanguageCode" class="text-danger small"></span>
+    </div>
+
+    <div class="mb-3">
+        <label asp-for="Subject" class="form-label fw-semibold">Subject</label>
+        <input asp-for="Subject" class="form-control" />
+        <span asp-validation-for="Subject" class="text-danger small"></span>
+    </div>
+
+    <div class="mb-3">
+        <label asp-for="HtmlBody" class="form-label fw-semibold">HTML Body</label>
+        <textarea asp-for="HtmlBody" class="form-control font-monospace" rows="10"></textarea>
+        <span asp-validation-for="HtmlBody" class="text-danger small"></span>
+    </div>
+
+    <div class="mb-3">
+        <label asp-for="TextBody" class="form-label fw-semibold">Text Body</label>
+        <textarea asp-for="TextBody" class="form-control font-monospace" rows="5"></textarea>
+    </div>
+
+    <div class="mb-3">
+        <label asp-for="VariablesJson" class="form-label fw-semibold">Variables (JSON)</label>
+        <textarea asp-for="VariablesJson" class="form-control font-monospace" rows="4"
+                  placeholder='[{"name":"UserName","required":true}]'></textarea>
+        <span asp-validation-for="VariablesJson" class="text-danger small"></span>
+        <div class="form-text">JSON array of <code>{"name":"...", "required":true|false}</code></div>
+    </div>
+
+    @section FormActions {
+        <button type="submit" class="btn btn-primary">💾 Save</button>
+        <a href="/admin/templates" class="btn btn-secondary">✖ Cancel</a>
+    }
+</form>