fix(disk-cleanup): prune protected cleanup walks

[teknium1]

Summary

Disk-cleanup quick cleanup now prunes protected state trees before traversal, so the session-end sweep cannot recursively scan the Hermes checkout, venv, or vendor directories under HERMES_HOME.

Changes

• Replaces the HERMES_HOME.rglob("*") empty-dir sweep with an explicit post-order stack walk.
• Skips protected top-level trees (hermes-agent, plugins, skills, profiles, etc.) before descending.
• Prunes vendor/VCS/cache-heavy dirs such as node_modules, .git, venv, .venv, site-packages, and __pycache__ inside managed subtrees.
• Adds regression coverage for protected-tree pruning and managed empty-dir cleanup.

Validation

Check	Result
scripts/run_tests.sh tests/plugins/test_disk_cleanup_plugin.py	48 passed
py_compile for plugin + tests	passed
real-path temp HERMES_HOME probe	protected hermes-agent/node_modules/.../empty stayed; managed scratch/ emptied
git diff --check origin/main..HEAD	passed

Closes #46601.
Salvages #46610 with @BlackishGreen33's authorship preserved.

Infographic

[github-actions]

🔎 Lint report: salvage/disk-cleanup-prune-walks vs origin/main

ruff

Total: 0 on HEAD, 0 on base (➖ 0)

🆕 New issues: none

✅ Fixed issues: none

Unchanged: 0 pre-existing issues carried over.

ty (type checker)

Total: 10905 on HEAD, 10905 on base (➖ 0)

🆕 New issues: none

✅ Fixed issues: none

Unchanged: 5738 pre-existing issues carried over.

Diagnostics are surfaced as warnings — this check never fails the build.