feat(agent): cross-char search_items tool + bump timeouts

Adds an MCP tool wrapping the inventory-service /search/items endpoint
with include_all_characters=true, so questions like 'find me a bracelet
with Legendary Acid Ward on any unequipped char' resolve in ONE tool call
instead of looping get_inventory over 60+ chars (which timed out at 120s).

- agent/tools.py: search_items_global wrapper
- agent/mcp_overlord.py: register new tool with detailed schema doc
- agent/claude_wrapper.py: include in --allowed-tools whitelist;
  bump timeout 120s -> 240s
- nginx/overlord.conf: bump /api/agent/ proxy timeout 180s -> 300s
- CLAUDE.md: brief Claude to USE search_items for cross-char searches

nginx/overlord.conf

@@ -64,8 +64,11 @@ server {
         proxy_set_header     X-Forwarded-For   $proxy_add_x_forwarded_for;
         proxy_set_header     X-Forwarded-Proto $scheme;
         proxy_pass_request_headers on;
-        proxy_read_timeout   180s;
-        proxy_send_timeout   180s;
+        # Heavy tool calls (cross-char search, suitbuilder) can take a while;
+        # the python wrapper caps each turn at 240s, so 300s gives some
+        # headroom for the round trip.
+        proxy_read_timeout   300s;
+        proxy_send_timeout   300s;
     }
 
     # API endpoints (live, trails, history, stats) — short-lived HTTP