v0.81.0: retire drive-activation banner; add standalone "Kiszolgáló újraindítása" button

In the intermediary-mount model an enrolled drive binds live into the running
guest (no reboot), so the "… meghajtó aktiválásra vár / Újraindítás most" banner
was an obsolete relic — also dead since v0.78 (pendingActivationDrives keyed on
the raw MountPath vs the now-stable sp.Path). Removed the banner block +
activatePendingDrives JS (settings.html), the PendingDrives feed (handlers.go),
and the dead pendingActivationDrives helper + its unused internal/system import.

Renamed handleStorageActivate -> HandleServerReboot (split out a testable
serverReboot core), removed the /api/storage/activate case, and mounted the
handler at the new non-storage route /api/server/reboot (RequireAuth+CsrfProtect).
The agent GuestReboot primitive is reused unchanged.

Added the standalone "Kiszolgáló újraindítása" settings card (sibling to the
controller-only "Vezérlő újraindítása"), reusing the pollRestart() loop.

Test: TestHandleServerReboot_CallsGuestReboot (fake diskAgent asserts GuestReboot
invoked once + 202). diskAgent/mockAgent gained GuestReboot.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_017PsnU2ASocYrvzqE82YDYW

controller/internal/web/storage_handlers_test.go

@@ -40,6 +40,8 @@ type mockAgent struct {
 	formatCalls       []formatCall
 	guestAttachCalls  []string
 	decommissionCalls []string
+	guestRebootCalls  int
+	guestRebootErr    error
 }
 
 type assignCall struct{ uuid, where, fstype string }
@@ -71,6 +73,10 @@ func (m *mockAgent) GuestAttach(_ context.Context, where string) error {
 	m.guestAttachCalls = append(m.guestAttachCalls, where)
 	return nil
 }
+func (m *mockAgent) GuestReboot(context.Context) error {
+	m.guestRebootCalls++
+	return m.guestRebootErr
+}
 
 func testServer(t *testing.T) *Server {
 	t.Helper()
@@ -255,6 +261,38 @@ func TestHandleStorageRegister_RegistersStablePath(t *testing.T) {
 	}
 }
 
+// TestHandleServerReboot_CallsGuestReboot exercises the standalone "Kiszolgáló újraindítása" core:
+// it must invoke the agent's GuestReboot exactly once and return the 202 envelope. (The HTTP handler
+// HandleServerReboot delegates to this core after building the live agent client — same split-out
+// pattern as runStorageInit, so the fake diskAgent can be injected here.)
+func TestHandleServerReboot_CallsGuestReboot(t *testing.T) {
+	s := testServer(t)
+	agent := &mockAgent{}
+	req := httptest.NewRequest(http.MethodPost, "/api/server/reboot", nil)
+	rr := httptest.NewRecorder()
+
+	s.serverReboot(rr, req, agent)
+
+	if agent.guestRebootCalls != 1 {
+		t.Fatalf("expected GuestReboot invoked exactly once, got %d", agent.guestRebootCalls)
+	}
+	if rr.Code != http.StatusAccepted {
+		t.Fatalf("expected 202 Accepted, got %d (body %s)", rr.Code, rr.Body.String())
+	}
+	var resp struct {
+		OK   bool `json:"ok"`
+		Data struct {
+			Rebooting bool `json:"rebooting"`
+		} `json:"data"`
+	}
+	if err := json.Unmarshal(rr.Body.Bytes(), &resp); err != nil {
+		t.Fatalf("decode response: %v", err)
+	}
+	if !resp.OK || !resp.Data.Rebooting {
+		t.Fatalf("expected {ok:true, data.rebooting:true}, got %+v", resp)
+	}
+}
+
 func TestFSUUIDForDevice(t *testing.T) {
 	disks := agentapi.DisksResponse{Disks: []agentapi.DiskInfo{
 		{BackingDevice: "/dev/sda1", DurableID: "uuid:AAAA"},