perf(agent): replace blocking file bridge with ZFT2

[Lanlan13-14]

Summary

• replace Worker SAB/Atomics + sync XHR file bridge with ZFT2 binary WebSocket
• complete remote RDPEFS IRPs asynchronously in Go WASM
• add bounded 8-request flow control, cancellation, ACL binding, session watchdog, and binary Agent writes
• pipeline sequential reads with 4 x 1 MiB bounded read-ahead
• remove Base64/sync-XHR file-transfer main paths

Verification

• ZFT2 Node tests: 19/19
• Go WASM tests: pass
• Go WASM production build: pass
• JavaScript syntax: pass
• Dart ZFT2 codec analyze: pass
• full Flutter/Android compile delegated to Agent PR CI; local sandbox is aarch64 while official Linux Flutter SDK is x64

Known pre-existing tests

• two RDP pipeline contract tests already fail on origin/main
• saved Telnet WS test is timing-sensitive under full parallel suite and passes independently