Fix dead MCP server URLs: deepsense rehosted, paypal moved to SSE (#239)

The Check MCP URLs workflow (after the connection-failure probe fix in
this PR's parent) surfaced four endpoints that fail every connection:

- mcp.deepsense.ai does not resolve in DNS at all. The biorxiv, chembl,
  and clinical_trials servers were rehosted under
  hcls.mcp.claude.com (Anthropic MCP directory entries dated
  2026-01-07). Paths are unchanged; only the host moved. All three
  return a complete MCP initialize response with no auth.

- mcp.paypal.com/mcp returns 404 at every path. PayPal's live endpoint
  is /sse (SSE transport, not streamable HTTP) and returns 401 with
  WWW-Authenticate: Bearer realm="OAuth" — alive, OAuth required.
  Their docs claim /http for streamable transport but it returns 404
  today. Type changed http -> sse to match the actual transport.

Anyone with the bio-research or small-business bundle installed gets
connect failures on every agent spawn until this lands.

bio-research/.mcp.json

@@ -8,10 +8,22 @@
       "type": "http",
       "url": "https://mcp.services.biorender.com/mcp"
     },
+    "biorxiv": {
+      "type": "http",
+      "url": "https://hcls.mcp.claude.com/biorxiv/mcp"
+    },
     "consensus": {
       "type": "http",
       "url": "https://mcp.consensus.app/mcp"
     },
+    "c-trials": {
+      "type": "http",
+      "url": "https://hcls.mcp.claude.com/clinical_trials/mcp"
+    },
+    "chembl": {
+      "type": "http",
+      "url": "https://hcls.mcp.claude.com/chembl/mcp"
+    },
     "synapse": {
       "type": "http",
       "url": "https://mcp.synapse.org/mcp"

small-business/.mcp.json

@@ -5,7 +5,7 @@
       "url": "https://ai-inc.quickbooks.intuit.com/v1/mcp"
     },
     "paypal": {
-      "type": "http",
+      "type": "sse",
       "url": "https://mcp.paypal.com/sse"
     },
     "hubspot": {