fix(paths): route achievements plugin + profile-tui through HERMES_HOME

Four callsites hardcoded Path.home() / '.hermes' with no HERMES_HOME
check, breaking Docker deployments and profile isolation (hermes -p):

- plugins/hermes-achievements/dashboard/plugin_api.py:
  state_path(), snapshot_path(), checkpoint_path() bare-literal paths
- scripts/profile-tui.py:
  DEFAULT_STATE_DB and DEFAULT_LOG defaults ignored HERMES_HOME
- hermes_cli/slack_cli.py:
  except-Exception fallback for slack-manifest.json dump
- optional-skills/migration/openclaw-migration/scripts/openclaw_to_hermes.py:
  --target argparse default

Use get_hermes_home() (with an ImportError shim for the standalone
scripts) or 'os.environ.get("HERMES_HOME") or str(Path.home()/".hermes")'
where importing hermes_constants is impractical.

E2E-verified: with HERMES_HOME=/tmp/x all three achievements paths and
both profile-tui defaults route under /tmp/x.

Salvaged from #18068 (original scope was broader mechanical cleanup
claiming 23 callsites were buggy; most were already respecting
HERMES_HOME via os.environ.get(key, default) — only these 4 had no env
check at all). Credit: @web-dev0521.

hermes_cli/slack_cli.py

@@ -18,6 +18,7 @@ for reinstall when scopes/commands change.
 from __future__ import annotations
 
 import json
+import os
 import sys
 from pathlib import Path
 
@@ -128,7 +129,7 @@ def slack_manifest_command(args) -> int:
 
                 target = Path(get_hermes_home()) / "slack-manifest.json"
             except Exception:
-                target = Path.home() / ".hermes" / "slack-manifest.json"
+                target = Path(os.environ.get("HERMES_HOME") or str(Path.home() / ".hermes")) / "slack-manifest.json"
         else:
             target = Path(write_target).expanduser()
         target.parent.mkdir(parents=True, exist_ok=True)