fix: expand tilde in get_hermes_home() when HERMES_HOME=~/... (#478)

Path('~/foo') does NOT expand ~. When HERMES_HOME=~/custom-path,
get_hermes_home() returned a Path with literal ~ which broke
all downstream path resolution.

Fix: add .expanduser() to the return value.

Closes #478

hermes_constants.py

@@ -14,7 +14,7 @@ def get_hermes_home() -> Path:
     Reads HERMES_HOME env var, falls back to ~/.hermes.
     This is the single source of truth — all other copies should import this.
     """
-    return Path(os.getenv("HERMES_HOME", Path.home() / ".hermes"))
+    return Path(os.getenv("HERMES_HOME", str(Path.home() / ".hermes"))).expanduser()
 
 
 def get_optional_skills_dir(default: Path | None = None) -> Path: