fix(security): batch 3 — issues #498-#499

[chaliy]

Summary

• security: MountableFs missing validate_path(), misc VFS gaps (TM-DOS-046, TM-DOS-049, TM-DOS-050) #498 (TM-DOS-046): Add validate_path() to all MountableFs write methods — path depth/character validation no longer bypassed for mounted filesystems
• security: MountableFs missing validate_path(), misc VFS gaps (TM-DOS-046, TM-DOS-049, TM-DOS-050) #498 (TM-DOS-049): Add explicit depth parameter to collect_dirs_recursive, capped by filesystem max_path_depth
• security: MountableFs missing validate_path(), misc VFS gaps (TM-DOS-046, TM-DOS-049, TM-DOS-050) #498 (TM-DOS-050): Propagate caller-configured parser limits through parse_word_string via new parse_word_string_with_limits() method
• security: Python BashTool.reset() drops security config (TM-PY-028) #499 (TM-PY-028): BashTool.reset() now preserves username, hostname, max_commands, and max_loop_iterations — matching PyBash.reset() behavior

Test plan

• All 21 security audit regression tests pass (4 new tests for batch 3)
• Full Rust test suite passes (cargo test --all-features — 1515+ tests)
• cargo fmt --check clean
• cargo clippy --all-targets --all-features -- -D warnings clean
• Python lint clean (ruff check + ruff format --check)
• Python test added for BashTool.reset() config preservation

Closes #498, closes #499

https://claude.ai/code/session_01TTiLUJVtmMNAo1NC9aQTn1