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_account_market_services.py

@@ -69,19 +69,19 @@ class FakeSpotClient:
 
 
 class AccountMarketServicesTestCase(unittest.TestCase):
-    def test_account_overview_and_dust_filter(self):
+    def test_get_balances_with_dust_flag(self):
         config = {
             "market": {"default_quote": "USDT"},
             "trading": {"dust_usdt_threshold": 10.0},
         }
-        payload = account_service.get_overview(
+        payload = account_service.get_balances(
             config,
             spot_client=FakeSpotClient(),
         )
-        self.assertEqual(payload["overview"]["total_equity_usdt"], 720.1)
-        symbols = {item["symbol"] for item in payload["positions"]}
-        self.assertNotIn("DOGEUSDT", symbols)
-        self.assertIn("BTCUSDT", symbols)
+        balances = {item["asset"]: item for item in payload["balances"]}
+        self.assertFalse(balances["USDT"]["is_dust"])
+        self.assertFalse(balances["BTC"]["is_dust"])
+        self.assertTrue(balances["DOGE"]["is_dust"])
 
     def test_market_tickers_and_scan_universe(self):
         config = {