fix(email): derive the Google OAuth redirect URI scheme from the request (#5995)

Both the authorize and callback routes built the redirect URI with a
hardcoded `http://` and the Host header. Behind any TLS terminator that
produces `http://host:443/api/email/oauth/google/callback` — the wrong
scheme and, on a split-port setup, a dead port. Google then refuses the
authorize request or the token exchange, so OAuth email is unusable on
every HTTPS deployment unless GOOGLE_OAUTH_REDIRECT_URI is pinned by hand.

uvicorn's proxy-headers middleware already rewrites the scheme from
X-Forwarded-Proto for trusted proxies (on by default, trusting 127.0.0.1),
so request.url.scheme is correct both directly and behind a proxy.

Google requires the callback's redirect_uri to match the authorize one
exactly, so both sites change together. An explicit
GOOGLE_OAUTH_REDIRECT_URI still wins, unchanged.

routes/email_routes.py

@@ -5954,7 +5954,7 @@ def setup_email_routes():
             raise HTTPException(400, "GOOGLE_OAUTH_CLIENT_ID not set — add it to .env")
         redirect_uri = (
             os.environ.get("GOOGLE_OAUTH_REDIRECT_URI")
-            or f"http://{request.headers.get('host', 'localhost:7000')}/api/email/oauth/google/callback"
+            or f"{request.url.scheme}://{request.headers.get('host', 'localhost:7000')}/api/email/oauth/google/callback"
         )
         state = make_oauth_state(account_id, owner)
         params = urllib.parse.urlencode({
@@ -5991,7 +5991,7 @@ def setup_email_routes():
         client_secret = os.environ.get("GOOGLE_OAUTH_CLIENT_SECRET", "")
         redirect_uri = (
             os.environ.get("GOOGLE_OAUTH_REDIRECT_URI")
-            or f"http://{request.headers.get('host', 'localhost:7000')}/api/email/oauth/google/callback"
+            or f"{request.url.scheme}://{request.headers.get('host', 'localhost:7000')}/api/email/oauth/google/callback"
         )
         import httpx as _httpx
         try: