Add first-class ChatGPT subscription provider support (#881)

* Add first-class ChatGPT subscription provider support

* Address PR feedback: move uuid import to top, reuse parsed config in up()

* Add ChatGPT token watchdog for seamless long-lived sessions

* Address PR feedback: error on stream=false for ChatGPT, fix auth file permissions

* Replace ChatGPT watchdog/restart with passthrough_auth

---------

Co-authored-by: Musa Malik <musam@uw.edu>

cli/planoai/chatgpt_cmd.py

@@ -0,0 +1,86 @@
+"""
+CLI commands for ChatGPT subscription management.
+
+Usage:
+    planoai chatgpt login    - Authenticate with ChatGPT via device code flow
+    planoai chatgpt status   - Check authentication status
+    planoai chatgpt logout   - Remove stored credentials
+"""
+
+import datetime
+
+import click
+from rich.console import Console
+
+from planoai import chatgpt_auth
+
+console = Console()
+
+
+@click.group()
+def chatgpt():
+    """ChatGPT subscription management."""
+    pass
+
+
+@chatgpt.command()
+def login():
+    """Authenticate with your ChatGPT subscription using device code flow."""
+    try:
+        auth_record = chatgpt_auth.login()
+        account_id = auth_record.get("account_id", "unknown")
+        console.print(
+            f"\n[green]Successfully authenticated with ChatGPT![/green]"
+            f"\nAccount ID: {account_id}"
+            f"\nCredentials saved to: {chatgpt_auth.CHATGPT_AUTH_FILE}"
+        )
+    except Exception as e:
+        console.print(f"\n[red]Authentication failed:[/red] {e}")
+        raise SystemExit(1)
+
+
+@chatgpt.command()
+def status():
+    """Check ChatGPT authentication status."""
+    auth_data = chatgpt_auth.load_auth()
+    if not auth_data or not auth_data.get("access_token"):
+        console.print(
+            "[yellow]Not authenticated.[/yellow] Run 'planoai chatgpt login'."
+        )
+        return
+
+    account_id = auth_data.get("account_id", "unknown")
+    expires_at = auth_data.get("expires_at")
+
+    if expires_at:
+        expiry_time = datetime.datetime.fromtimestamp(
+            expires_at, tz=datetime.timezone.utc
+        )
+        now = datetime.datetime.now(tz=datetime.timezone.utc)
+        if expiry_time > now:
+            remaining = expiry_time - now
+            console.print(
+                f"[green]Authenticated[/green]"
+                f"\n  Account ID: {account_id}"
+                f"\n  Token expires: {expiry_time.strftime('%Y-%m-%d %H:%M:%S UTC')}"
+                f" ({remaining.seconds // 60}m remaining)"
+            )
+        else:
+            console.print(
+                f"[yellow]Token expired[/yellow]"
+                f"\n  Account ID: {account_id}"
+                f"\n  Expired at: {expiry_time.strftime('%Y-%m-%d %H:%M:%S UTC')}"
+                f"\n  Will auto-refresh on next use, or run 'planoai chatgpt login'."
+            )
+    else:
+        console.print(
+            f"[green]Authenticated[/green] (no expiry info)"
+            f"\n  Account ID: {account_id}"
+        )
+
+
+@chatgpt.command()
+def logout():
+    """Remove stored ChatGPT credentials."""
+    chatgpt_auth.delete_auth()
+    console.print("[green]ChatGPT credentials removed.[/green]")