[client,android] Generate debug bundle to file (#7528)

* [client] Add a debug bundle file export to the Android bridge

The Android app can only upload a debug bundle and hand the user a key.
Users who want to inspect what leaves their device before sharing it
have no way to get the zip itself. Add DebugBundleFile, which generates
the bundle into the cache directory and returns its path instead of
uploading; the app copies it wherever the user chose and removes it.

DebugBundle keeps its behavior. Both entry points share the unexported
debugBundle with an upload switch, so the body stays where it was and
merges cleanly with the MDM overlay change on main.

Because the file variant leaves the zip to the caller and the upload
variant only removes it after the upload finishes, a process killed in
between leaves a zip behind in the cache. Remove stale bundles before
generating a new one: RemoveStaleBundles deletes zips matching the
generator's pattern that are older than an hour. Remote debug jobs write
to the same directory, so younger files are treated as still in use.

* Preserve network map for debug bundle on Android

* [client] Keep exported Android debug bundles out of the stale cleanup

DebugBundleFile hands the zip to the caller, but the file kept the
netbird.debug.*.zip name that RemoveStaleBundles matches, so a later
debug run could delete it once it was older than an hour. Rename the
exported bundle to netbird.debug-file.*.zip after generation so the
cleanup only ever touches bundles no caller owns.

* [client] Warn when a stale debug bundle cannot be removed

A failed removal means bundles pile up in the cache directory, so log it
at Warn instead of Debug. A file that is already gone was removed by a
concurrent cleanup and is skipped silently.

* [client] Drop the outdated debugBundle comment

The comment still said the file variant leaves the zip in place, but it
is renamed by debug.ExportBundle since the stale-cleanup change.

* [client] Test that the network map reaches the debug bundle

Cover both halves of the path Android now relies on: the engine keeps
the latest sync response once persistence is enabled, and the bundle
generator writes it to network_map.json (anonymized or not) and omits
the file when there is no sync response.

* [client] Remove abandoned exported debug bundles after a day

An exported bundle is owned by the caller, but if the app is killed
before it copies and deletes the file, nothing ever removes it from the
cache directory. Let RemoveStaleBundles also match exported bundles,
with a 24 hour max age instead of the caller-provided one, so a bundle
that is still being saved survives while an abandoned one goes.

client/internal/engine_test.go

@@ -1493,3 +1493,21 @@ func TestOverlayAddrsFromAllowedIPs(t *testing.T) {
 		})
 	}
 }
+
+func TestEngine_SyncResponsePersistence(t *testing.T) {
+	e := &Engine{}
+
+	_, err := e.GetLatestSyncResponse()
+	require.Error(t, err, "persistence is disabled by default")
+
+	e.SetSyncResponsePersistence(true)
+	e.persistSyncResponse(&mgmtProto.SyncResponse{NetworkMap: &mgmtProto.NetworkMap{Serial: 7}})
+
+	got, err := e.GetLatestSyncResponse()
+	require.NoError(t, err)
+	assert.Equal(t, uint64(7), got.GetNetworkMap().GetSerial())
+
+	e.SetSyncResponsePersistence(false)
+	_, err = e.GetLatestSyncResponse()
+	require.Error(t, err)
+}