Add workflow registry for background goroutine lifecycle management

Ultraworked with [Sisyphus](https://github.com/code-yeongyu/claude-agent)

Co-authored-by: Sisyphus <clio-agent@sisyphuslabs.ai>

internal/workflow_registry.go

@@ -0,0 +1,100 @@
+package internal
+
+import (
+	"context"
+	"fmt"
+	"sync"
+	"time"
+
+	"homelab.lan/music-agregator/internal/eventbus"
+)
+
+type WorkflowEntry struct {
+	ID      string
+	AlbumID string
+	Quality string
+	Ctx     context.Context
+	Cancel  context.CancelFunc
+	Topic   string
+	Ready   chan struct{}
+}
+
+type WorkflowRegistry struct {
+	mu        sync.Mutex
+	workflows map[string]*WorkflowEntry
+	bus       *eventbus.EventBus
+	wg        sync.WaitGroup
+}
+
+func NewWorkflowRegistry(bus *eventbus.EventBus) *WorkflowRegistry {
+	return &WorkflowRegistry{
+		workflows: make(map[string]*WorkflowEntry),
+		bus:       bus,
+	}
+}
+
+func workflowKey(albumID, quality string) string {
+	return fmt.Sprintf("%s:%s", albumID, quality)
+}
+
+func (r *WorkflowRegistry) GetOrCreate(ctx context.Context, albumID, quality string) (*WorkflowEntry, bool) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	key := workflowKey(albumID, quality)
+	if entry, ok := r.workflows[key]; ok {
+		return entry, false
+	}
+
+	wfCtx, cancel := context.WithCancel(ctx)
+	entry := &WorkflowEntry{
+		AlbumID: albumID,
+		Quality: quality,
+		Ctx:     wfCtx,
+		Cancel:  cancel,
+		Topic:   key,
+		Ready:   make(chan struct{}),
+	}
+	r.workflows[key] = entry
+	return entry, true
+}
+
+func (r *WorkflowRegistry) Remove(albumID, quality string) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	key := workflowKey(albumID, quality)
+	delete(r.workflows, key)
+}
+
+func (r *WorkflowRegistry) Get(albumID, quality string) (*WorkflowEntry, bool) {
+	r.mu.Lock()
+	defer r.mu.Unlock()
+
+	key := workflowKey(albumID, quality)
+	entry, ok := r.workflows[key]
+	return entry, ok
+}
+
+func (r *WorkflowRegistry) WaitGroup() *sync.WaitGroup {
+	return &r.wg
+}
+
+func (r *WorkflowRegistry) Shutdown(timeout time.Duration) {
+	r.mu.Lock()
+	for _, entry := range r.workflows {
+		entry.Cancel()
+	}
+	r.mu.Unlock()
+
+	done := make(chan struct{})
+	go func() {
+		r.wg.Wait()
+		close(done)
+	}()
+
+	select {
+	case <-done:
+	case <-time.After(timeout):
+	}
+}