Evict archive writers on deletion and sweep idle archives (closes #89) (#95)

Per-webhook archive writers are now evicted when the webhook or its last
database target is deleted, and a background sweeper prunes expired rows from
idle archives that no longer receive writes. Archive files themselves are never
deleted.

internal/handlers/handlers.go

@@ -51,6 +51,7 @@ type HandlersParams struct {
 	Healthcheck  *healthcheck.Healthcheck
 	Session      *session.Session
 	Notifier     delivery.Notifier
+	Evictor      delivery.WebhookEvictor
 }
 
 // Handlers provides HTTP handler methods for all application
@@ -63,6 +64,7 @@ type Handlers struct {
 	dbMgr     *database.WebhookDBManager
 	session   *session.Session
 	notifier  delivery.Notifier
+	evictor   delivery.WebhookEvictor
 	templates map[string]*template.Template
 }
 
@@ -97,6 +99,7 @@ func New(
 	s.dbMgr = params.WebhookDBMgr
 	s.session = params.Session
 	s.notifier = params.Notifier
+	s.evictor = params.Evictor
 
 	// Parse all page templates once at startup
 	s.templates = map[string]*template.Template{