fix(skills): ship google-workspace deps as [google] extra; make setup.py 3.9-parseable

Closes #13626.

Two follow-ups on top of the _hermes_home helper from @jerome-benoit's #12729:

1. Declare a [google] optional extra in pyproject.toml
   (google-api-python-client, google-auth-oauthlib, google-auth-httplib2) and
   include it in [all]. Packagers (Nix flake, Homebrew) now ship the deps by
   default, so `setup.py --check` does not need to shell out to pip at
   runtime — the imports succeed and install_deps() is never reached.
   This fixes the Nix breakage where pip/ensurepip are stripped.

2. Add `from __future__ import annotations` to setup.py so the PEP 604
   `str | None` annotation parses on Python 3.9 (macOS system python).
   Previously system python3 SyntaxError'd before any code ran.

install_deps() error message now also points users at the extra instead of
just the raw pip command.

pyproject.toml

@@ -78,6 +78,15 @@ termux = [
 ]
 dingtalk = ["dingtalk-stream>=0.20,<1", "alibabacloud-dingtalk>=2.0.0", "qrcode>=7.0,<8"]
 feishu = ["lark-oapi>=1.5.3,<2", "qrcode>=7.0,<8"]
+google = [
+  # Required by the google-workspace skill (Gmail, Calendar, Drive, Contacts,
+  # Sheets, Docs).  Declared here so packagers (Nix, Homebrew) ship them with
+  # the [all] extra and users don't hit runtime `pip install` paths that fail
+  # in environments without pip (e.g. Nix-managed Python).
+  "google-api-python-client>=2.100,<3",
+  "google-auth-oauthlib>=1.0,<2",
+  "google-auth-httplib2>=0.2,<1",
+]
 # `hermes dashboard` (localhost SPA + API).  Not in core to keep the default install lean.
 web = ["fastapi>=0.104.0,<1", "uvicorn[standard]>=0.24.0,<1"]
 rl = [
@@ -110,6 +119,7 @@ all = [
   "hermes-agent[voice]",
   "hermes-agent[dingtalk]",
   "hermes-agent[feishu]",
+  "hermes-agent[google]",
   "hermes-agent[mistral]",
   "hermes-agent[bedrock]",
   "hermes-agent[web]",