fix(providerresolve): add debug logging for background provider resolution

- Log loaded system_configs (background.provider, agent.default_provider)
- Log provider lookup attempts with source and error details
- Warn when falling back to first registered provider
- Surface config load errors instead of silently swallowing them

Helps diagnose provider resolution failures in episodic/vault workers.

internal/providerresolve/background_provider.go

@@ -2,6 +2,7 @@ package providerresolve
 
 import (
 	"context"
+	"log/slog"
 
 	"github.com/google/uuid"
 	"github.com/nextlevelbuilder/goclaw/internal/providers"
@@ -25,40 +26,59 @@ func ResolveBackgroundProvider(
 	var configs map[string]string
 	if systemConfigs != nil {
 		tctx := store.WithTenantID(ctx, tenantID)
-		configs, _ = systemConfigs.List(tctx)
+		var err error
+		configs, err = systemConfigs.List(tctx)
+		if err != nil {
+			slog.Warn("background: failed to load system_configs", "tenant", tenantID, "error", err)
+		} else {
+			slog.Debug("background: loaded system_configs",
+				"tenant", tenantID,
+				"background.provider", configs["background.provider"],
+				"agent.default_provider", configs["agent.default_provider"])
+		}
 	}
 
 	// tryResolve attempts to get a provider by name
-	tryResolve := func(name, model string) (providers.Provider, string, bool) {
+	tryResolve := func(name, model, source string) (providers.Provider, string, bool) {
 		if name == "" {
 			return nil, "", false
 		}
 		p, err := registry.GetForTenant(tenantID, name)
 		if err != nil || p == nil {
+			slog.Debug("background: provider not found",
+				"source", source, "name", name, "tenant", tenantID, "error", err)
 			return nil, "", false
 		}
 		if model == "" {
 			model = p.DefaultModel()
 		}
+		slog.Debug("background: resolved provider",
+			"source", source, "name", name, "model", model, "tenant", tenantID)
 		return p, model, true
 	}
 
 	// 1. Explicit background config
-	if p, m, ok := tryResolve(configs["background.provider"], configs["background.model"]); ok {
+	if p, m, ok := tryResolve(configs["background.provider"], configs["background.model"], "background.provider"); ok {
 		return p, m
 	}
 	// 2. Agent default provider
-	if p, m, ok := tryResolve(configs["agent.default_provider"], configs["agent.default_model"]); ok {
+	if p, m, ok := tryResolve(configs["agent.default_provider"], configs["agent.default_model"], "agent.default_provider"); ok {
 		return p, m
 	}
-	// 3. First registered provider
+	// 3. First registered provider (fallback)
 	names := registry.ListForTenant(tenantID)
 	if len(names) == 0 {
+		slog.Warn("background: no providers available", "tenant", tenantID)
 		return nil, ""
 	}
 	p, err := registry.GetForTenant(tenantID, names[0])
 	if err != nil {
+		slog.Warn("background: fallback provider failed", "tenant", tenantID, "name", names[0], "error", err)
 		return nil, ""
 	}
+	slog.Warn("background: using fallback provider (no explicit config)",
+		"tenant", tenantID, "provider", names[0], "available", names,
+		"background.provider", configs["background.provider"],
+		"agent.default_provider", configs["agent.default_provider"])
 	return p, p.DefaultModel()
 }