fix(security): restore .env/auth.json/state.db with 0600 perms

`hermes import` was creating secret files with the process umask
(typically 0644) instead of 0600. zipfile.open() does not honor the
Unix mode bits stored in zip member external_attr; the restore loop
used open(target, "wb") which always falls back to umask.

Threat: silent privilege downgrade after a routine restore on
multi-user systems (shared dev boxes, CI runners, jump hosts) — any
local user could read API keys and OAuth tokens from ~/.hermes/.

Fix mirrors the convention already used at file creation
(hermes_cli/auth.py: stat.S_IRUSR | stat.S_IWUSR for auth.json).
The quick-snapshot restore path (restore_quick_snapshot) is
unaffected — it uses shutil.copy2 which preserves perms via
copystat().

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

hermes_cli/backup.py

@@ -61,6 +61,9 @@ _EXCLUDED_NAMES = {
     "cron.pid",
 }
 
+# zipfile.open() drops Unix mode bits on extract; restore tightens these to 0600.
+_SECRET_FILE_NAMES = {".env", "auth.json", "state.db"}
+
 
 def _should_exclude(rel_path: Path) -> bool:
     """Return True if *rel_path* (relative to hermes root) should be skipped."""
@@ -381,6 +384,8 @@ def run_import(args) -> None:
                 target.parent.mkdir(parents=True, exist_ok=True)
                 with zf.open(member) as src, open(target, "wb") as dst:
                     dst.write(src.read())
+                if target.name in _SECRET_FILE_NAMES:
+                    os.chmod(target, 0o600)
                 restored += 1
             except (PermissionError, OSError) as exc:
                 errors.append(f"  {rel}: {exc}")