Rebuild complex multistage vulnerability chains

[March-77]

Summary

• independently rebuild the five complex/multistage chains requested by issue 【2026犀牛鸟】重建整体错位和多阶段利用样本的调用链 #7
• move n8n, OpenClaw, Langflow, and FastMCP annotations from defaults, declarations, guards, and logs to attacker input, failed validation, and final security-impacting uses
• explicitly document prerequisite and main-trigger stages for Git-operation and media TOCTOU scenarios
• provide a backward-compatible schema recommendation instead of adding mandatory fields
• include a reproducible multi-repository builder, five-entry patch, field diff, empty unresolved-review queue, rationale report, and tests

Rebuilt entries

• entry-00185: workflow fileName -> missing Git metadata restriction -> fsWriteFile
• entry-00197: prepared/retargeted media path -> /media/:id trigger -> boundary checks -> handle read
• entry-00290: patch text -> dangling-symlink fallback -> fileOps.writeFile
• entry-00320: multipart file.filename -> unsanitized storage join -> async_open
• entry-00391: LLM flat_args -> raw path replacement -> urljoin

Entries remain verify=0 for maintainer confirmation.

Validation

• 5 patch rows, 15 field-level diffs, 0 unresolved review rows
• 36/36 replacement nodes exactly match pinned source
• python -m unittest discover -s tests -p "test_rebuilt_chains.py" -v (4 tests)
• python -m py_compile scripts/build_rebuilt_chains.py
• git diff --check

Closes #7