Add invoice SMS notifications and customer intake kiosk

Invoice SMS:
- Send Invoice modal now prompts Email/SMS/Both based on customer contact data
- New /invoice/{token} customer-facing view page with full line items and pay button
- PublicViewToken (permanent) added to Invoice; separate from expiring PaymentLinkToken
- InvoiceSent SMS default template added; customizable via Notification Templates settings
- {{viewUrl}} placeholder documented in template editor

Customer Intake Kiosk:
- Tablet kiosk flow: Contact → Job → Terms/Signature → Confirmation
- Remote link mode for off-site customers (lighter form, no signature)
- KioskHub (AllowAnonymous SignalR) for staff-to-tablet push without login
- Staff activates tablet via cookie; sends remote link manually
- Submitted sessions create Customer + Job automatically; fires in-app notification

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

src/PowderCoating.Web/Hubs/KioskHub.cs

@@ -0,0 +1,55 @@
+using Microsoft.AspNetCore.Authorization;
+using Microsoft.AspNetCore.SignalR;
+using Microsoft.Extensions.Logging;
+
+namespace PowderCoating.Web.Hubs;
+
+/// <summary>
+/// SignalR hub that delivers "StartIntake" push events to the front-desk tablet.
+/// Deliberately [AllowAnonymous] — the tablet runs without a logged-in user.
+/// Security is enforced at the kiosk route level via the KioskActivationToken cookie.
+///
+/// On connect the tablet passes ?companyId=N in the hub URL query string; this hub
+/// places that connection in the company-scoped group "kiosk-{companyId}" so that
+/// KioskController.StartSession can push to exactly that company's tablet.
+/// </summary>
+[AllowAnonymous]
+public class KioskHub : Hub
+{
+    private readonly ILogger<KioskHub> _logger;
+
+    /// <summary>Initialises the hub with the required logger.</summary>
+    public KioskHub(ILogger<KioskHub> logger)
+    {
+        _logger = logger;
+    }
+
+    /// <summary>
+    /// Joins the connection to the company-scoped kiosk group on connect.
+    /// companyId is read from the ?companyId query param embedded in the hub URL by the Welcome view.
+    /// </summary>
+    public override async Task OnConnectedAsync()
+    {
+        try
+        {
+            var companyId = Context.GetHttpContext()?.Request.Query["companyId"].FirstOrDefault();
+            if (!string.IsNullOrEmpty(companyId))
+                await Groups.AddToGroupAsync(Context.ConnectionId, $"kiosk-{companyId}");
+        }
+        catch (Exception ex)
+        {
+            _logger.LogError(ex, "Error in KioskHub.OnConnectedAsync for connection {ConnectionId}", Context.ConnectionId);
+        }
+
+        await base.OnConnectedAsync();
+    }
+
+    /// <summary>Logs unexpected disconnects (e.g. tablet going to sleep).</summary>
+    public override async Task OnDisconnectedAsync(Exception? exception)
+    {
+        if (exception != null)
+            _logger.LogWarning(exception, "KioskHub client disconnected with error: {ConnectionId}", Context.ConnectionId);
+
+        await base.OnDisconnectedAsync(exception);
+    }
+}