Fix managed stream reconnects

[ross-rl]

Summary

• keep managed ACP streams re-subscribing on unexpected SSE EOF/error using the last seen Axon sequence
• keep Claude connection read loops reconnecting after repeated graceful stream closes instead of stopping after one retry
• update reconnect tests and README behavior docs

Verification

• bun run --filter '@runloop/remote-agents-sdk' test src/acp/axon-stream.test.ts src/claude/connection.test.ts
• bun run check
• bun run typecheck
• bun run build
• bun run test