fix(api): route analytics handlers through read pool

The four /api/analytics/* endpoints (timeline, summary, top-agents,
top-channels) all ran their SELECT queries on the write pool
(MaxOpenConns=1, serialized) and would time out at 125s with
context-canceled whenever a long writer (e.g. dream dispatch) held the
single connection. Summary swallows the error and returns {0,0,0}, so
the dashboard rendered an empty-cluster lie.

Plumb ReadDB through RouterConfig from main, fall back to DB if the
read pool is unset, and pass it to NewAnalyticsHandler. Same shape as
the /readyz fix in b03350f.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

cmd/synapbus/main.go

@@ -865,6 +865,7 @@ func runServe(cmd *cobra.Command, args []string) error {
 		Broadcaster:       sseBroadcaster,
 		SessionMiddleware: sessionMiddleware,
 		DB:                db.DB,
+		ReadDB:            db.QueryDB(),
 		Version:           version,
 		PushService:       pushService,
 		TrustService:      trustService,

internal/api/analytics_handler.go

@@ -21,6 +21,8 @@ type AnalyticsHandler struct {
 }
 
 // NewAnalyticsHandler creates a new analytics handler.
+// db should be the read pool — every query in this handler is read-only and
+// must not block on the serialized write pool.
 func NewAnalyticsHandler(db *sql.DB, agentService *agents.AgentService, channelService *channels.Service) *AnalyticsHandler {
 	return &AnalyticsHandler{
 		db:             db,

internal/api/router.go

@@ -52,8 +52,12 @@ type RouterConfig struct {
 	Broadcaster       *SSEBroadcaster
 	SessionMiddleware func(http.Handler) http.Handler
 	DB                *sql.DB
-	Version           string
-	BaseURL           string
+	// ReadDB is the read-only connection pool (query_only=ON, MaxOpenConns>1).
+	// Read-only API handlers must use this to avoid blocking on the serialized
+	// write pool. If nil, handlers fall back to DB.
+	ReadDB  *sql.DB
+	Version string
+	BaseURL string
 
 	// CoreMemoryStore (feature 020 — US2) wires the per-(owner, agent)
 	// core memory REST endpoints. Nil → routes not registered.
@@ -324,9 +328,14 @@ func NewRouterWithConfig(cfg RouterConfig) chi.Router {
 		})
 	}
 
-	// Analytics (authenticated, requires DB)
+	// Analytics (authenticated, requires DB). Reads must use the read pool so
+	// dashboard queries don't serialize behind long-running writers.
 	if cfg.DB != nil {
-		analyticsHandler := NewAnalyticsHandler(cfg.DB, cfg.AgentService, cfg.ChannelService)
+		analyticsDB := cfg.ReadDB
+		if analyticsDB == nil {
+			analyticsDB = cfg.DB
+		}
+		analyticsHandler := NewAnalyticsHandler(analyticsDB, cfg.AgentService, cfg.ChannelService)
 		r.Group(func(r chi.Router) {
 			r.Use(authMiddleware)