Fix ObjC server-mode premature TCP close and CI linker error

[Copilot]

When used as an HTTP server (e.g. KTVHTTPCache), the socket sends a TCP FIN after every writeData: call, killing the connection before the response body is transmitted. Separately, CI fails to link due to missing Security framework.

nw_connection_send premature close

is_complete was true, signaling end-of-stream after each write. HTTP servers that send headers and body in separate writes get the connection torn down between them — client sees -1005 NSURLErrorNetworkConnectionLost.

// Before: closes write side after every send
nw_connection_send(conn, data, ctx, true, ...);

// After: stream stays open for subsequent writes
nw_connection_send(conn, data, ctx, false, ...);

disconnectAfterWriting / disconnectAfterReading were no-ops

Both just called [self disconnect] immediately, cancelling in-flight writes. Now tracks pendingWriteCount and defers teardown until the last send completion fires. Same pattern for reads via flagDisconnectAfterReads.

Missing -framework Security in CI

sec_protocol_options_set_verify_block (TLS verify block) lives in Security.framework. Added to CI build command, main.m build comment, and README.

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