ihasmail 2.0: rebuild as Stalwart-first JMAP webmail

Replace the FastAPI/HTMX prototype with a Node/Hono session proxy and a
React 19/Vite SPA. Mail (conversation view, search operators, labels,
sanitised HTML, privacy image proxy, invites, undo send, templates),
calendar (month/week/day/agenda, invites, free/busy, categories,
context menus), contacts (JSContact, groups, vCard), files, Sieve filter
builder (incl. filter-from-message with retroactive apply), vacation,
identities with default + Reply-To, PWA/mobile layout, push via SSE,
in-memory mock Stalwart for dev, Docker + CI.

nginx.example.conf

@@ -0,0 +1,19 @@
+# Example nginx location block for ihasmail behind TLS termination.
+server {
+    listen 443 ssl http2;
+    server_name mail.example.com;
+    # ssl_certificate ...; ssl_certificate_key ...;
+
+    client_max_body_size 60m;
+
+    location / {
+        proxy_pass http://127.0.0.1:8080;
+        proxy_http_version 1.1;
+        proxy_set_header Host $host;
+        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+        proxy_set_header X-Forwarded-Proto $scheme;
+        # Server-Sent Events (push notifications)
+        proxy_buffering off;
+        proxy_read_timeout 3600s;
+    }
+}