feat(web): C2 Parts 2+3 — POST /backup/tier2/restore + "Fájlok visszaállítása" button

- Endpoint next to /backup/restore; handler mirrors backupRestoreHandler
  (ParseForm → validStackName → backupMgr guard → WARN with RemoteAddr →
  RestoreTier2Files → flash). Flash strings: "<stack>: N fájl visszaállítva a
  másodlagos másolatból." / "Nincs hiányzó fájl — minden fájl megvan a helyén."
  / "Fájl-visszaállítás sikertelen: <err>" (refusals carry the Hungarian
  reasons from the engine).
- backups.html: the button on the healthy Tier-2 layer row only (the
  Tier2Configured branch already excludes disconnected/inactive; additionally
  gated on Tier2LastRun), inline POST form with CSRF + confirm dialog naming
  the additive-only semantics and the last-copy timestamp. Template gates
  (id + emoji) green.
- Handler guard test (C6): traversal/empty → exact Hungarian flash, no work
  started (nil backupMgr would panic if reached).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01PSK5g6qYLknKj8u3QAFEr6

controller/internal/web/tier2_restore_handler_test.go

@@ -0,0 +1,50 @@
+package web
+
+import (
+	"io"
+	"log"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strings"
+	"testing"
+)
+
+// postTier2Restore drives the handler with a form body, as the UI's inline form does.
+func postTier2Restore(t *testing.T, s *Server, stackName string) *httptest.ResponseRecorder {
+	t.Helper()
+	form := url.Values{"stack_name": {stackName}}
+	req := httptest.NewRequest(http.MethodPost, "/backup/tier2/restore", strings.NewReader(form.Encode()))
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+	rec := httptest.NewRecorder()
+	s.backupTier2RestoreHandler(rec, req)
+	return rec
+}
+
+// TestTier2RestoreHandler_Guards proves Scenario C6 + the missing-param guard: traversal and empty
+// names are rejected with the exact Hungarian flash BEFORE any restore work (backupMgr is nil here —
+// reaching it would panic, so a pass also proves no work started).
+func TestTier2RestoreHandler_Guards(t *testing.T) {
+	s := &Server{logger: log.New(io.Discard, "", 0)} // backupMgr nil on purpose
+
+	for name, want := range map[string]string{
+		"../../etc": "%C3%89rv%C3%A9nytelen+alkalmaz%C3%A1sn%C3%A9v", // Érvénytelen alkalmazásnév
+		"a/b":       "%C3%89rv%C3%A9nytelen+alkalmaz%C3%A1sn%C3%A9v",
+		"":          "Hi%C3%A1nyz%C3%B3+param%C3%A9terek", // Hiányzó paraméterek
+	} {
+		rec := postTier2Restore(t, s, name)
+		if rec.Code != http.StatusFound {
+			t.Errorf("%q: status = %d, want 302", name, rec.Code)
+			continue
+		}
+		if loc := rec.Header().Get("Location"); !strings.Contains(loc, want) {
+			t.Errorf("%q: redirect = %q, want flash %q", name, loc, want)
+		}
+	}
+
+	// Valid name but no backup manager → the not-configured flash (still no panic, no work).
+	rec := postTier2Restore(t, s, "nextcloud")
+	if loc := rec.Header().Get("Location"); !strings.Contains(loc, "Ment%C3%A9s+nincs+be%C3%A1ll%C3%ADtva") {
+		t.Errorf("nil backupMgr: redirect = %q", loc)
+	}
+}