Refactor: implement centralized HERMES_HOME environment variable support (#892)

[Nebula037]

What does this PR do?

This PR centralizes the resolution of the agent's base directory by introducing a global HERMES_HOME constant. It enables users to override the default ~/.hermes path using the HERMES_HOME environment variable, which is critical for containerized deployments (Docker/Podman), CI/CD pipelines, and multi-instance management.

Related Issue

Fixes #892

Type of Change

• ♻️ Refactor (no behavior change)

Changes Made

• hermes_constants.py: Added get_hermes_home() utility and exported HERMES_HOME as a pathlib.Path object.
• tools/process_registry.py: Refactored to import HERMES_HOME from constants, replacing the localized path resolution for the processes.json checkpoint file.

How to Test

1. Verify Default Path: Run the agent without the environment variable; it should still default to ~/.hermes.
2. Verify Override: Set export HERMES_HOME=/tmp/hermes_test and start the agent.
3. Check Checkpoint: Run a background process via the terminal tool and verify that processes.json is created in /tmp/hermes_test/ instead of the home directory.

Checklist

Code

• I've read the Contributing Guide
• My commit messages follow Conventional Commits
• I searched for existing PRs to make sure this isn't a duplicate
• My PR contains only changes related to this fix/feature
• I've run pytest tests/ -q and all tests pass (N/A for browser-only refactor, relying on CI)
• I've added tests for my changes
• I've tested on my platform: GitHub Codespaces / Browser

Documentation & Housekeeping

• I've updated relevant documentation (docstrings in hermes_constants.py)
• I've considered cross-platform impact (Windows, macOS) using pathlib

[teknium1]

Closing — the issue this targets (#892) is already fully resolved. All 9 files listed in the issue already import get_hermes_home() from hermes_cli/config.py and use it correctly. No hardcoded ~/.hermes paths remain in any of them (fixed by earlier PRs #51 and #538).

This PR would introduce a second get_hermes_home() in hermes_constants.py alongside the existing one in hermes_cli/config.py, creating a duplicate source of truth. Appreciate the effort though — thanks for looking into this!