Adds active-HERMES_HOME control-plane files to the write deny list:
auth.json, config.yaml, webhook_subscriptions.json, and any path
under mcp-tokens/. realpath() resolves before comparison so
directory-traversal and symlink targets are normalised, preventing
trivial deny-list bypass via ../ tricks.
Without this, a prompt-injected agent could rewrite Hermes' own
auth state or routing config via write_file / patch — without
triggering the terminal dangerous-command approval — and persist
attacker-controlled behaviour across sessions.
Fixes#14072
build_write_denied_paths() resolved the protected ``.env`` via
get_hermes_home(), which is profile-aware. When a profile is active
HERMES_HOME points at ``<root>/profiles/<name>`` and ``hermes_home / ".env"``
expands to the *profile* env file only — the global ``<root>/.env`` is left
off the deny list and a write_file call against it succeeds. Since the
top-level .env supplies credentials inherited by every profile, this is a
P0 credential-exfiltration / overwrite path.
Add a parallel ``_hermes_root_path()`` helper that returns the Hermes root
(via the existing ``get_default_hermes_root()`` constant) and include
``<root>/.env`` in the deny list alongside ``<active_profile>/.env``. Both
paths now refuse write_file/patch regardless of profile state. The active
HERMES_HOME .env entry is preserved so the protection in non-profile mode
is unchanged.
A regression test exercises the profile-active scenario by pointing
HERMES_HOME at ``<tmp>/profiles/coder`` and asserting that ``<tmp>/.env``
is denied.
Fixes#15981
