DeepSeek V4-Flash news enrichment: LLM sentiment, surprise direction, summary

Three display/warning-only upgrades to the news engine, all behind the
existing keyword path as fallback — signals are never gated on LLM
output (event_risk_caps_signals / sentiment_affects_signals stay False
per the 2026-07 audit; backtester use_news=False untouched):

- Headline sentiment: one batched call per 600s cache window (capped at
  25 new headlines, sha1-cached so repeats are never re-sent) overrides
  the keyword scores per currency with the gold-inverse doctrine encoded
  in the prompt.
- Release surprises: get_event_risk_level's description now says which
  way the print pulls GOLD ("— gold bearish: strong jobs lift yields"),
  fixing the documented numeric-only gap; risk level and windows
  unchanged.
- Market summary: 1-2 sentence macro blurb on SignalReport.news_summary,
  rendered in Telegram alerts (📰) and the CLI (🧠).

New llm_client.py: requests-only OpenAI-compatible client (no SDK), one
attempt per call, UTC-day request cap, singleton so the cap survives
per-scan NewsEngine reconstruction. Config: deepseek block in
config.json + DEEPSEEK_API_KEY env; absent key = fully inert.

Live-measured API behavior baked in: V4-Flash is a hybrid thinking model
— requests send thinking:disabled (reasoning otherwise blew the timeout
and could exhaust max_tokens before the answer); prompts are static
module constants so DeepSeek's prefix cache prices repeat calls at the
cache-hit rate; scores use compact [s, xau] pairs; timeout 12s.

Tests 273 → 286 (new Module 19 + deepseek config tests).

Co-Authored-By: Claude Fable 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Nsd8HcrV67GbCZXxZEn1Ma

config.json.example

@@ -33,5 +33,12 @@
     "quality_gate": "C",
     "max_hold_bars": 300
   },
+  "deepseek": {
+    "api_key": "REPLACE_WITH_YOUR_DEEPSEEK_API_KEY_OR_EMPTY",
+    "model": "deepseek-v4-flash",
+    "enabled": true,
+    "timeout_seconds": 12,
+    "daily_request_cap": 500
+  },
   "log_level": "INFO"
 }