refactor: remove Dex local-password invite provisioning (ADR-019)

Authentik owns invites now (infra ADR-0001). Delete adapters/dex, the
/invite set-password UI, the tapir invite CLI, the InvitationStore/
DexPasswordCreator ports + App wiring, the invite Templ pages, and the
invite Taskfile target. New users are invited via Authentik, log in via
OIDC, and hit the existing /register gate. invitations table (mig 009)
left in place (append-only; harmless). task check green.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

internal/web/view.go

@@ -183,11 +183,6 @@ func statusURL(videoID string) templ.SafeURL {
 	return templ.SafeURL("/v/" + videoID + "/status")
 }
 
-// inviteURL builds the claim path (POST) for an invite token.
-func inviteURL(token string) templ.SafeURL {
-	return templ.SafeURL("/invite/" + token)
-}
-
 // Charmbracelet-inspired palette for the summarizing animation (TapirSpinner) —
 // a charm purple box, pink tapir, mint snout/eyes/progress. Kept as named consts
 // so the inline span colours and the CSS track/fill share one source of truth.
@@ -338,12 +333,11 @@ type flashView struct {
 // flashMessages maps each flash code to its banner. An unknown code renders no
 // banner (flashFor returns ok=false), so a forged cookie value is inert.
 var flashMessages = map[string]flashView{
-	flashConnected:      {"success", "YouTube account connected."},
-	flashConnectFailed:  {"error", "Could not connect your YouTube account. Please try again."},
-	flashDisconnected:   {"success", "Account disconnected."},
-	flashDeleted:        {"success", "Your account and all its data were deleted."},
-	flashRegistered:     {"success", "Welcome to Tapir — your account is ready."},
-	flashAccountCreated: {"success", "Account created — log in with your email and password."},
+	flashConnected:     {"success", "YouTube account connected."},
+	flashConnectFailed: {"error", "Could not connect your YouTube account. Please try again."},
+	flashDisconnected:  {"success", "Account disconnected."},
+	flashDeleted:       {"success", "Your account and all its data were deleted."},
+	flashRegistered:    {"success", "Welcome to Tapir — your account is ready."},
 }
 
 func flashFor(code string) (flashView, bool) {