refactor(V2): get_instruments common-only on /mcp (enriched with Deribit filters)

Move get_instruments off the per-exchange Deribit router and onto the
unified interface, without losing the advanced Deribit filtering.

- /mcp/tools/get_instruments now accepts the Deribit-specific filters
  (currency, kind, expiry_from/to, strike_min/max, min_open_interest) and
  pagination (offset/limit). Venues that list everything (Hyperliquid)
  ignore them. Response adds `meta: {deribit: {total, offset, limit,
  has_more}}` surfacing per-source pagination.
- Remove /mcp-deribit/tools/get_instruments (endpoint + tool wrapper +
  GetInstrumentsReq schema). The DeribitClient.get_instruments METHOD
  stays — it's what the unified normalizer calls.

Tests: cover the enriched filters + meta passthrough; app-boot asserts
/mcp-deribit/tools/get_instruments is gone. Docs (API_REFERENCE/README/
CLAUDE) and smoke updated; also fixed the stale Hyperliquid tool count
(14 → 15) found during the doc check.

325 passed, ruff clean. Verified live: kind=option limit=5 → 5/940
has_more=true; /mcp-deribit/tools/get_instruments → 404.

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

tests/integration/test_app_boot.py

@@ -30,7 +30,8 @@ def test_app_boots_and_health_responds(monkeypatch):
     assert "/mcp/tools/get_instruments" in paths
     assert "/mcp/tools/get_historical" in paths
     assert "/mcp/tools/get_indicators" in paths
-    # get_historical / get_indicators are common-only, not per-exchange
+    # get_instruments / get_historical / get_indicators are common-only
+    assert "/mcp-deribit/tools/get_instruments" not in paths
     assert "/mcp-deribit/tools/get_historical" not in paths
     assert "/mcp-deribit/tools/get_technical_indicators" not in paths
     assert "/mcp-hyperliquid/tools/get_historical" not in paths