refactor(workers): per-tenant provider resolution for background workers

Replace static provider/model fields with per-tenant resolution at
processing time. Fixes architectural mismatch where singleton workers
used tenant-specific system_configs.

Changes:
- Add shared ResolveBackgroundProvider() in providerresolve package
- Refactor vault enrichWorker, episodic, dreaming workers to resolve
  provider per-event using registry + systemConfigs
- Remove hot-reload machinery (no longer needed)
- Update ConsolidationDeps to use Registry/SystemConfigs

Fallback chain: background.provider → agent.default_provider → first
registered provider.

internal/providerresolve/background_provider.go

@@ -0,0 +1,64 @@
+package providerresolve
+
+import (
+	"context"
+
+	"github.com/google/uuid"
+	"github.com/nextlevelbuilder/goclaw/internal/providers"
+	"github.com/nextlevelbuilder/goclaw/internal/store"
+)
+
+// ResolveBackgroundProvider resolves the LLM provider for background workers.
+// Fallback chain: background.provider → agent.default_provider → first registered.
+// Used by vault enrichment, episodic summarization, dreaming consolidation.
+func ResolveBackgroundProvider(
+	ctx context.Context,
+	tenantID uuid.UUID,
+	registry *providers.Registry,
+	systemConfigs store.SystemConfigStore,
+) (providers.Provider, string) {
+	if registry == nil {
+		return nil, ""
+	}
+
+	// Load system configs for the tenant
+	var configs map[string]string
+	if systemConfigs != nil {
+		tctx := store.WithTenantID(ctx, tenantID)
+		configs, _ = systemConfigs.List(tctx)
+	}
+
+	// tryResolve attempts to get a provider by name
+	tryResolve := func(name, model string) (providers.Provider, string, bool) {
+		if name == "" {
+			return nil, "", false
+		}
+		p, err := registry.GetForTenant(tenantID, name)
+		if err != nil || p == nil {
+			return nil, "", false
+		}
+		if model == "" {
+			model = p.DefaultModel()
+		}
+		return p, model, true
+	}
+
+	// 1. Explicit background config
+	if p, m, ok := tryResolve(configs["background.provider"], configs["background.model"]); ok {
+		return p, m
+	}
+	// 2. Agent default provider
+	if p, m, ok := tryResolve(configs["agent.default_provider"], configs["agent.default_model"]); ok {
+		return p, m
+	}
+	// 3. First registered provider
+	names := registry.ListForTenant(tenantID)
+	if len(names) == 0 {
+		return nil, ""
+	}
+	p, err := registry.GetForTenant(tenantID, names[0])
+	if err != nil {
+		return nil, ""
+	}
+	return p, p.DefaultModel()
+}