fix: batch additional small open PR fixes

[syhya]

Summary

This PR bundles several small, high-confidence open PR fixes into one mergeable patch:

1. Hookify Write/Edit field mapping fix (from fix(hookify): make file rules match Write tool content #24321)

   • Aligns content / new_text / new_string extraction so Write rules using new_text work as expected.

2. Python 3.8 typing compatibility (from fix: Python 3.8 compatibility in hookify config_loader #24266)

   • Replaces tuple[...] annotation with Tuple[...] in config_loader.py.

3. README install wording update for WSL (from misc: Update installation instructions for WSL support #27126)

   • Changes “MacOS/Linux (Recommended)” to “MacOS/Linux/WSL (Recommended)”.

4. Plugin marketplace entry example (from fix(plugin-dev): add marketplace.json entry example in create-plugin #24509)

   • Adds a concrete JSON snippet to create-plugin.md guidance.

5. Duplicate-handling scripts exit code fix (from Fix exit codes for duplicate automation scripts #25309)

   • Ensures caught async errors set process.exitCode = 1 in both scripts.

6. IPv6 firewall hardening (from fix(devcontainer): let init-firewall.sh block IPv6 traffic #24951, enhanced)

   • Sets default IPv6 drop policies when ip6tables is available.
   • Wrapped with command -v ip6tables guard to avoid failures in environments without ip6tables.

Validation

• python -m py_compile plugins/hookify/core/config_loader.py plugins/hookify/core/rule_engine.py
• bash -n .devcontainer/init-firewall.sh
• Hookify field-mapping smoke assertion for Write/Edit extraction paths

Notes

These are intentionally small and isolated fixes to reduce review overhead and help move the open PR backlog.