feat(V2): unified /mcp interface; retire Bybit/Alpaca to old/

Add a common cross-exchange interface (/mcp) over the integrated venues
(deribit, hyperliquid):

- get_instruments: uniform schema where each row carries its own
  `exchange`, `fees` (maker/taker, live from Deribit, null where the
  venue has no per-instrument schedule) and `history_start` (listing
  date, live from Deribit creation_timestamp), plus type/tick_size and a
  lossless `native` blob. Optional `exchange` filter; fan-out otherwise.
- get_historical: generalized to {exchange, instrument, interval,
  start_date, end_date}, returning a single chosen venue's candles.
  Consensus merge stays available on /mcp-cross.

New: routers/unified.py, exchanges/cross/instruments.py (normalizers),
UnifiedClient in cross/client.py, schemas in cross/tools.py. Deribit
get_instruments now also surfaces maker/taker_commission and
creation_timestamp (additive).

Retire Bybit and Alpaca from the API surface: move clients, routers,
settings classes and their tests under old/ (history preserved via
git mv); drop them from the builder, /mcp-cross dispatch and symbol_map.
Bybit remains a public funding/OI data source in sentiment (not the
trading client). IBKR is intentionally excluded from /mcp for now.

Docs: rewrite API_REFERENCE.md (remove Bybit/Alpaca, document /mcp,
clarify that data_timestamp is injected globally by middleware).

Tests: add unified-interface coverage; update cross/settings/builder/boot
tests for the reduced venue set. Fix a pre-existing flaky assertion in
the Hyperliquid signing test (r/s use eth_utils.to_hex like the official
SDK, so a leading zero byte yields <66 chars ~1/256 of the time).

323 passed, ruff clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/cerbero_mcp/__main__.py

@@ -21,14 +21,13 @@ from cerbero_mcp.client_registry import ClientRegistry
 from cerbero_mcp.common.logging import configure_root_logging
 from cerbero_mcp.exchanges import build_client
 from cerbero_mcp.routers import (
-    alpaca,
-    bybit,
     cross,
     deribit,
     hyperliquid,
     ibkr,
     macro,
     sentiment,
+    unified,
 )
 from cerbero_mcp.server import build_app
 from cerbero_mcp.settings import Settings
@@ -66,13 +65,12 @@ def _make_app(settings: Settings) -> FastAPI:
     app.router.lifespan_context = lifespan
 
     app.include_router(deribit.make_router())
-    app.include_router(bybit.make_router())
     app.include_router(hyperliquid.make_router())
-    app.include_router(alpaca.make_router())
     app.include_router(ibkr.make_router())
     app.include_router(macro.make_router())
     app.include_router(sentiment.make_router())
     app.include_router(cross.make_router())
+    app.include_router(unified.make_router())
     app.include_router(admin.make_admin_router())
 
     return app