Improve the mesh SDK with public mesh discovery, blocking APIs, and native examples

[i386]

Summary

• Let Rust, Swift, and Kotlin SDK consumers discover all public meshes on Nostr, smart-auto connect to the best public mesh, or join a specific discovered mesh by invite token.
• Add blocking mesh client APIs and real invite-token mesh transport so native SDK smoke tests exercise model listing and chat over the mesh instead of a localhost-only fallback.
• Expand the native SDK surface with clearer FFI errors, refreshed generated bindings, a Swift owner-key helper, and a tested Swift example runner for the example app.

SDK

• Add mesh-api discovery helpers for public mesh queries, smart auto-connect, and building a client from a discovered mesh.
• Extend the UniFFI surface with public mesh query/result DTOs plus auto-connect helpers.
• Update the Swift and Kotlin wrappers, docs, and generated bindings to expose the new discovery and connect flows.

Runtime

• Replace the embedded client's localhost-only path with invite-token mesh transport in mesh-client, including model listing and chat over the mesh connection.
• Add blocking join, list-models, status, disconnect, and reconnect helpers used by the FFI worker thread.
• Tighten native smoke behavior so the live SDK test picks a model that is actually returned by the mesh.

Swift Example

• Add a reusable MeshExampleRunner and unit tests for the Swift example app.
• Add a Swift helper to generate owner keypair bytes for the example flow.
• Update the XCFramework build script to better support the example and release packaging flow.

Testing

• cargo fmt --all -- --check
• cargo test -p mesh-api -p mesh-api-ffi --lib --tests
• cargo test -p mesh-llm-client --lib --tests
• ./sdk/kotlin/scripts/generate-kotlin-bindings.sh
• ./sdk/swift/scripts/generate-swift-bindings.sh