feat: add production headless monitoring

[domcyrus]

Versioned JSONL and JSON snapshots for explicit headless monitoring, stacked on #599 and related to #9.

• Rejects collisions between redirected stdout and JSON, PCAP, sidecar, or PCAPNG outputs before RustNet truncates or writes them. Includes inherited-descriptor regressions.
• Coalesces pending snapshots before serialization, preserving terminal records and bounded shutdown. JSONL remains sampled state, not complete traffic history; English, Chinese, and Japanese guides explain separate PCAP collection, export errors, and resource costs.
• Retains the modular frontend, stable connection IDs, explicit rate units, and existing Windows console support. Verification details and performance limitations accompany the branch update.

[domcyrus]

Updated through b34f7aa, preserving the foundation history.

• Fixed redirected-stdout collisions with all artifact types, with inherited non-truncating descriptor tests. Final combined-head CI passed, including Windows and FreeBSD.
• Pending snapshots now coalesce before serialization. With 19 offered rich 50k-connection snapshots and the same two records written, median CPU fell 2.438s to 1.731s (29%, three paired repetitions). Peak RSS was 408.1 to 408.9 MiB; fast-output CPU ranges overlapped.
• Combined workspace tests passed on macOS. Snapshot semantics remain unchanged; English, Chinese, and Japanese documentation explains PCAP usage, export errors, and resource limits. Projection cost and overload loss remain possible.

Final stacked Linux smoke: all 399,744 generated datagrams appeared exactly once in both independent and RustNet PCAPs. JSONL matched all 1,000 stable flows and their packet/byte counters, with zero reported drops/export errors and clean shutdown. This is workload-specific validation, not a complete-history guarantee.