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

provider/nofxos/ai500_cache_test.go

@@ -0,0 +1,86 @@
+package nofxos
+
+import (
+	"errors"
+	"testing"
+	"time"
+)
+
+func withStubbedAI500Fetch(t *testing.T, fn func(c *Client) ([]CoinData, error)) {
+	t.Helper()
+	original := fetchAI500ListFn
+	fetchAI500ListFn = fn
+	ai500Cache.mu.Lock()
+	ai500Cache.coins = nil
+	ai500Cache.fetchedAt = time.Time{}
+	ai500Cache.mu.Unlock()
+	t.Cleanup(func() {
+		fetchAI500ListFn = original
+		ai500Cache.mu.Lock()
+		ai500Cache.coins = nil
+		ai500Cache.fetchedAt = time.Time{}
+		ai500Cache.mu.Unlock()
+	})
+}
+
+func TestGetAI500ListCachedWithinTTL(t *testing.T) {
+	calls := 0
+	withStubbedAI500Fetch(t, func(c *Client) ([]CoinData, error) {
+		calls++
+		return []CoinData{{Pair: "BTCUSDT", Score: 95.5}}, nil
+	})
+
+	client := NewClient("", "")
+	first, err := GetAI500ListCached(client)
+	if err != nil {
+		t.Fatalf("first call: %v", err)
+	}
+	second, err := GetAI500ListCached(client)
+	if err != nil {
+		t.Fatalf("second call: %v", err)
+	}
+	if calls != 1 {
+		t.Fatalf("fetch calls = %d, want 1 (second call must hit cache)", calls)
+	}
+	if len(first) != 1 || len(second) != 1 || second[0].Pair != "BTCUSDT" {
+		t.Fatalf("unexpected results: first=%v second=%v", first, second)
+	}
+}
+
+func TestGetAI500ListCachedServesStaleOnError(t *testing.T) {
+	calls := 0
+	withStubbedAI500Fetch(t, func(c *Client) ([]CoinData, error) {
+		calls++
+		if calls == 1 {
+			return []CoinData{{Pair: "ETHUSDT", Score: 88}}, nil
+		}
+		return nil, errors.New("API returned status 429")
+	})
+
+	client := NewClient("", "")
+	if _, err := GetAI500ListCached(client); err != nil {
+		t.Fatalf("first call: %v", err)
+	}
+
+	ai500Cache.mu.Lock()
+	ai500Cache.fetchedAt = time.Now().Add(-2 * ai500CacheTTL)
+	ai500Cache.mu.Unlock()
+
+	coins, err := GetAI500ListCached(client)
+	if err != nil {
+		t.Fatalf("expected stale data instead of error, got: %v", err)
+	}
+	if len(coins) != 1 || coins[0].Pair != "ETHUSDT" {
+		t.Fatalf("expected stale ETH entry, got %v", coins)
+	}
+}
+
+func TestGetAI500ListCachedErrorsWithoutCache(t *testing.T) {
+	withStubbedAI500Fetch(t, func(c *Client) ([]CoinData, error) {
+		return nil, errors.New("upstream down")
+	})
+
+	if _, err := GetAI500ListCached(NewClient("", "")); err == nil {
+		t.Fatal("expected error when upstream fails with empty cache")
+	}
+}