feat: add Hyperliquid WebSocket and Solana gRPC streaming endpoints

[user1303836]

Summary

• Add real-time streaming infrastructure with 3 new endpoints: POST /v1/stream/start, POST /v1/stream/{stream_id}/stop, GET /v1/streams
• Support Hyperliquid WebSocket streaming via existing HyperliquidWsClient (subscribes to userFills, userFundings, userNonFundingLedgerUpdates)
• Support Solana gRPC streaming via existing SolanaGrpcAdapter (Yellowstone)
• Batch-flush ingested transactions (100 items or 5-second interval)
• Semaphore-based concurrency limiting (max 5 concurrent streams)
• CancellationToken for clean stream shutdown
• Add solana_grpc_url and solana_grpc_token config fields
• Add Clone derive on Repository for spawned task usage
• 13 new tests covering all stream endpoints, auth, wallet scoping, semaphore limits, and serialization (189 total tests pass)

Changed files

• api/src/main.rs - streaming handlers, routes, StreamEntry/StreamInfo structs, run_hyperliquid_stream, run_solana_stream, tests
• api/Cargo.toml - add tokio-util, chrono dependencies
• core/src/config.rs - add solana_grpc_url, solana_grpc_token fields
• adapters/src/repo.rs - add #[derive(Clone)] to Repository

Test plan

• All 189 tests pass (cargo test)
• cargo clippy -- -D warnings clean
• cargo fmt -- --check clean
• Verify Hyperliquid WS streaming against mainnet (requires live wallet)
• Verify Solana gRPC streaming against a Yellowstone endpoint (requires solana_grpc_url configured)

[user1303836]

Closing: PR #94 already merged Solana gRPC streaming with the shared stream infrastructure. This PR's Hyperliquid WS streaming additions conflict with that merged code. Filed as a future enhancement issue instead.