fix: map subtitle label field in protobuf bridge

[schobiDotDev]

Closes #109

Problem

stremio-core#947 (v0.55.0) added a label: Option<String> field to the Subtitles struct, allowing addons to provide custom display names for subtitle tracks. However, the protobuf bridge doesn't map this field, so Android/Android TV apps never receive it.

Currently, the protobuf name field (field 4) is populated with the addon name via addon_name.cloned(), not the subtitle's own label.

Changes

1. subtitle.proto: Added optional string label = 5 to the Subtitle message
2. subtitle.rs: Map Subtitles.label to the new protobuf label field in both ToProtobuf and FromProtobuf
3. Cargo.lock: Updated stremio-core dependency from 9a827fdd to b5d3833f to pick up the label field on the Subtitles struct

The existing name field (field 4) is left unchanged - it continues to carry the addon name. The new label field (field 5) is additive and backward compatible.

Related

• stremio-core#947 - Added label to Subtitles type
• stremio-web#1166 - Companion fix for web client
• stremio-bugs#544 - Android TV subtitle name issues

Android app follow-up

Once this bridge change is merged, the Android app's subtitle picker would need to prefer label over the resolved lang name for variant display. Since the app is closed source, this would be handled by the Stremio team.