config: drop the dead oanda.account_id (auto-execution leftover), keep it tolerated

The candle provider needs only oanda.api_token + base_url; account_id belonged to the
auto-execution daemon removed 2026-09-03 (31002cb). Removed from config.json.example and
the unused oanda_account_id() accessor deleted; the key stays in _KNOWN_OANDA so existing
config.json files keep loading. CLAUDE.md env-var list updated. Test locks all three.

Suite: 464 passed.

Claude-Session: https://claude.ai/code/session_01RWV2yLt3YXHHGVYHSQU2EE

test_all.py

@@ -10491,6 +10491,21 @@ def _():
         os.remove(path)
 
 
+@test("app_config: legacy oanda.account_id is tolerated and ignored (auto-execution removed 2026-09-03)")
+def _():
+    import copy
+    import app_config as _ac
+    payload = copy.deepcopy(_FULL_CFG)
+    payload.setdefault("oanda", {})["account_id"] = "101-004-LEGACY-001"
+    payload["oanda"].setdefault("api_token", "tok")
+    app = load_app_config(_write_json(payload))          # must NOT raise
+    assert app.oanda_settings.get("api_token") == payload["oanda"]["api_token"]
+    assert not hasattr(_ac, "oanda_account_id"), "dead accessor must stay deleted"
+    assert "account_id" not in open("config.json.example").read(), \
+        "the example must not advertise a key nothing reads"
+    assert _ac.oanda_api_token(app) == payload["oanda"]["api_token"]
+
+
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