fix(sandbox): drop deny rules that file permission checks never match

[potiuk]

Summary

• Write(.claude/settings.json) and Write(.claude/settings.local.json) looked like they
  guarded those two files, but file permission checks only match Edit(path) rules — a
  Write(...) deny rule is inert. Both paths are already covered by the Edit(...) deny rules
  immediately above, which apply to every file-editing tool, so removing the dead pair loses no
  protection and stops the settings block from implying a guard that was not there.
• Mirrors the removal into tools/sandbox-lint/expected.json, as every change to the live
  sandbox must be (docs/security/threat-model.md mitigation M.29).

Type of change

• Cross-cutting (RFC, AGENTS.md, sandbox, privacy-LLM)

Test plan

• prek run --all-files passes
• uv run pytest passes in tools/sandbox-lint — the baseline-vs-live drift check is the
  gate that catches an unmirrored settings change, and it fails without the expected.json
  half of this commit.

RFC-AI-0004 compliance

• Sandbox — strictly removes inert rules; no path gains write access that did not
  already have it.

Notes for reviewers

• Worth confirming the premise rather than the diff: if Write(path) deny rules are honoured
  somewhere I have not found, these two should stay and the Edit(...) pair is the redundant
  one. The behaviour I relied on is that file permission checks match only Edit(path), which
  covers all file-editing tools including Write.