docs: explain reverse-proxy geo-blocking on the browser landing page

The landing page served on GET to the MCP URL is the splash users see when
they open their connection URL in a browser. The most common "I see the
welcome page but my AI client can't connect" cause is a reverse-proxy/CDN
geo-blocking rule that drops US IP addresses, where most AI/LLM services
connect from (e.g. Anthropic's 160.79.104.0/21).

Add a section telling users that seeing this page means the URL is set up
correctly, that the block is on the proxy/CDN side rather than HA-MCP, and
pointing them at geo/country rules and their proxy access logs.

Closes homeassistant-ai#1669.

Author: kingpanther13

src/ha_mcp/__main__.py

@@ -993,6 +993,21 @@ def register_browser_landing(
         "connector or MCP settings of your AI/LLM client. No username or password required.\n"
         "Setup instructions: https://homeassistant-ai.github.io/ha-mcp/\n"
         "\n"
+        "--- Seeing this page? Your URL is set up correctly ---\n"
+        "\n"
+        "If this page loads in your browser, the MCP server is reachable and the\n"
+        "URL is correct. If your AI client still cannot connect, the problem is\n"
+        "not on HA-MCP's side -- it is likely due to your reverse proxy / CDN\n"
+        "(Cloudflare, NGINX, Traefik, etc.). The most common pitfall is geo /\n"
+        "country blocking: most AI/LLM services connect from US-based cloud\n"
+        "infrastructure, so if you block US IP addresses (or only allow your own\n"
+        "country), that is why your client cannot connect. Allow your provider's\n"
+        "IP ranges (or your client's egress IPs). For example, Claude.ai connects\n"
+        "from Anthropic's network, 160.79.104.0/21.\n"
+        "\n"
+        "Your proxy's access logs will show the blocked attempt -- look for the\n"
+        "request from your AI provider's IP (e.g. an Anthropic 160.79.x.x address).\n"
+        "\n"
         "--- Cloudflare Users ---\n"
         "\n"
         'If your LLM cannot connect, Cloudflare\'s "Block AI training bots"\n'

tests/src/unit/test_browser_landing.py

@@ -46,6 +46,9 @@ async def test_get_returns_405_with_helpful_message(mcp_app):
     assert "Block AI training bots" in resp.text
     assert '"do not block (allow crawlers)"' in resp.text
     assert "dash.cloudflare.com" in resp.text
+    # Reverse-proxy / geo-blocking guidance (issue #1669)
+    assert "Your URL is set up correctly" in resp.text
+    assert "160.79.104.0/21" in resp.text
     assert resp.headers["allow"] == "POST, DELETE"