feat(agent): surface the AI500 index board in chat, tools, and sidebar

- provider/nofxos: GetAI500ListCached — 5min TTL cache with stale
  fallback on upstream failure; ResolveClient routes through the claw402
  gateway when a wallet key is configured (user's claw402 model key ->
  CLAW402_WALLET_KEY env -> direct nofxos)
- new GET /api/ai500 endpoint serving the score-sorted board
- new get_ai500_list agent tool + prompt rule: when the user wants coin
  picks or creates a strategy without naming coins, consult AI500's
  high-scoring entries by default
- web: AI500 sidebar panel (rank, score badge, gain since entry,
  5min auto-refresh); clicking an entry asks the agent to analyze it

api/handler_ai500.go

@@ -0,0 +1,43 @@
+package api
+
+import (
+	"net/http"
+	"strconv"
+
+	"github.com/gin-gonic/gin"
+
+	"nofx/agent"
+)
+
+// handleAI500List serves the AI500 index board for the agent UI panel.
+// Data is fetched through the user's claw402 wallet when one is configured
+// (falling back to the direct nofxos client) and served from a 5-minute
+// cache, so panel polling never hammers the upstream.
+func (s *Server) handleAI500List(c *gin.Context) {
+	userID := c.GetString("user_id")
+
+	limit := 0
+	if raw := c.Query("limit"); raw != "" {
+		parsed, err := strconv.Atoi(raw)
+		if err != nil || parsed < 0 {
+			c.JSON(http.StatusBadRequest, gin.H{"error": "limit must be a non-negative integer"})
+			return
+		}
+		limit = parsed
+	}
+
+	walletKey := agent.Claw402WalletKeyForStoreUser(s.store, userID)
+	entries, err := agent.AI500Board(walletKey, limit)
+	if err != nil {
+		SafeInternalError(c, "Get AI500 list", err)
+		return
+	}
+
+	c.JSON(http.StatusOK, gin.H{
+		"success": true,
+		"data": gin.H{
+			"coins": entries,
+			"count": len(entries),
+		},
+	})
+}