refactor: flatten account command to a single balances view

Remove overview/balances/positions subcommands in favor of one
`account` command that returns all balances with an `is_dust` flag.
Add descriptions to every parser and expose -a/--agent and --doc
on all leaf commands for better help discoverability.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tests/test_cli.py

@@ -91,6 +91,25 @@ class CLITestCase(unittest.TestCase):
         self.assertIn("lastPrice", output)
         self.assertIn("BTCUSDT", output)
 
+    def test_account_dispatches(self):
+        captured = {}
+        with (
+            patch.object(
+                cli, "load_config", return_value={"binance": {"spot_base_url": "https://test", "recv_window": 5000}, "market": {"default_quote": "USDT"}, "trading": {"dust_usdt_threshold": 10.0}}
+            ),
+            patch.object(cli, "get_binance_credentials", return_value={"api_key": "k", "api_secret": "s"}),
+            patch.object(cli, "SpotBinanceClient"),
+            patch.object(
+                cli.account_service, "get_balances", return_value={"balances": [{"asset": "BTC", "is_dust": False}]}
+            ),
+            patch.object(
+                cli, "print_output", side_effect=lambda payload, **kwargs: captured.setdefault("payload", payload)
+            ),
+        ):
+            result = cli.main(["account"])
+        self.assertEqual(result, 0)
+        self.assertEqual(captured["payload"]["balances"][0]["asset"], "BTC")
+
     def test_upgrade_dispatches(self):
         captured = {}
         with (