Name each database target's archive for its webhook and target (closes #376)

Each database target now has its own archive file,
archive-WEBHOOKNAME-TARGETNAME-TARGETID.db, instead of one
archive-WEBHOOKID.db per webhook. delivery.ArchiveFileName builds the
name: each name is lowercased, keeps ASCII letters and digits, turns
every other run of characters into one dash, and is cut to 40
characters.

Renaming a webhook or a target renames its archive files under the
archive writer's lock, before the new name is saved, and back again if
the save fails. Deleting a target evicts only that target's writer.
Archive files are never deleted, and nothing looks for files under the
old name.

Model: opus-5-5

internal/handlers/handlers.go

@@ -62,7 +62,7 @@ type HandlersParams struct {
 	Session      *session.Session
 	Middleware   *middleware.Middleware
 	Notifier     delivery.Notifier
-	Evictor      delivery.WebhookEvictor
+	Archives     delivery.Archives
 	SSRFGuard    *delivery.Guard
 }
 
@@ -77,7 +77,7 @@ type Handlers struct {
 	session   *session.Session
 	mw        *middleware.Middleware
 	notifier  delivery.Notifier
-	evictor   delivery.WebhookEvictor
+	archives  delivery.Archives
 	mtr       *metrics.Set
 	templates map[string]*template.Template
 
@@ -128,7 +128,7 @@ func New(
 	s.session = params.Session
 	s.mw = params.Middleware
 	s.notifier = params.Notifier
-	s.evictor = params.Evictor
+	s.archives = params.Archives
 	s.mtr = metrics.Default()
 	s.ssrf = params.SSRFGuard