fix: docker proxy build and localize language-thread copy

[daopunk]

Summary

• Fix docker/Dockerfile.proxy so the registration-proxy image builds against the current Cargo workspace (stubs for signal-bot / signal-bot-core / signal-bot-transcription; drop retired crates).
• Keep Cargo registry retries / sparse index / longer HTTP timeout for more reliable crate downloads in Docker.
• Localize Language Thread sidecar title, description, and welcome via NEAR before create_group / invite (English target skips NEAR; failure falls back to English).
• Unblocks local Docker bring-up and smoke testing of the proxy path while we work toward a clean Phala CVM deploy.

Context

End state is Phala TEE deployment (translation / transcription CVMs + registration proxy as needed). Until that is solid, we need a Dockerfile that actually builds so we can troubleshoot pairing, Signal registration, and compose locally.

Test plan

• docker build -f docker/Dockerfile.proxy . succeeds
• Local compose/env using the proxy image starts without Dockerfile stub failures
• !translate-me-on es creates a sidecar whose name and welcome are Spanish (or English fallback if NEAR fails)
• Existing-sidecar join path (add_members) still works without re-creating the group