[Infra] Persist DataProtection keys in the DB (fixes logout/antiforgery on deploy)

Add Microsoft.AspNetCore.DataProtection.EntityFrameworkCore; AppDbContext implements IDataProtectionKeyContext with a DataProtectionKeys set; PersistKeysToDbContext + SetApplicationName(hamkadr). Now the key ring is shared across restarts/replicas, so auth cookies, antiforgery tokens and the captcha no longer break on every deploy (the root cause of the earlier admin lock-out). Migration: DataProtectionKeys table.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

src/JobsMedical.Web/Program.cs

@@ -3,6 +3,7 @@ using System.Text.Unicode;
 using JobsMedical.Web.Data;
 using JobsMedical.Web.Models;
 using JobsMedical.Web.Services;
+using Microsoft.AspNetCore.DataProtection;
 using Microsoft.AspNetCore.Authentication.Cookies;
 using Microsoft.AspNetCore.HttpOverrides;
 using Microsoft.AspNetCore.Mvc;
@@ -77,6 +78,13 @@ builder.Services.AddSingleton(HtmlEncoder.Create(
 builder.Services.AddDbContext<AppDbContext>(opt =>
     opt.UseNpgsql(builder.Configuration.GetConnectionString("Default")));
 
+// Persist the DataProtection key ring in the DB so antiforgery tokens, auth cookies and the
+// captcha survive deploys/restarts (otherwise a new key ring each boot logs everyone out and
+// breaks antiforgery — the cause of the earlier admin lock-out).
+builder.Services.AddDataProtection()
+    .PersistKeysToDbContext<AppDbContext>()
+    .SetApplicationName("hamkadr");
+
 var app = builder.Build();
 
 // Apply migrations + seed on startup (fine for MVP single-instance deploy).