Conformance: Stream/fs/http implementation gaps blocking upstream tests

[NathanFlurry]

Various upstream Node.js tests fail due to implementation gaps in bridged modules:

• fs: VFS doesn't support watch/watchFile, symlinks, permissions bits, BigInt stat fields, createReadStream/createWriteStream edge cases
• stream: Internal stream state behavior differs from Node.js (backpressure, error propagation, pipeline edge cases)
• http: Server request/response lifecycle edge cases, keep-alive, transfer encoding

Tracked via conformance test exclusions (category: implementation-gap).