chore: drop unreachable branches outside the signal core (no behaviour change)

- providers: _to_oanda_instrument / _to_tiingo_ticker / _to_td_symbol no longer
  guess a wire symbol for pairs that are not registered — the registries are
  the only source, so an unknown symbol raises the provider's DataIntegrityError
  instead of silently fetching something else. Every scanned symbol is validated
  against PAIR_INFO at import, so nothing reachable changes.
- main / telegram_bot _fmt_price: the sub-$10 five-decimal branch could never
  fire for gold.
- news_engine._parse_pair: BASE/QUOTE only; the Yahoo "=X" fallback was
  unreachable (its test goes with it).
- dashboard_publisher.event_to_dict: drop minutes_until (frozen at publish
  time, misleading) and is_high_impact — dashboard.js never read either.
- static/dashboard.html: unused id="cal-table".

Tried and reverted: trimming the LogRow fields nothing in analyze_signal_log
reads — the tests read them to verify the loader round-trips those DB columns,
so they stay.

Suite: 460 passed, 0 failed.

Claude-Session: https://claude.ai/code/session_0156YhogLytzj9P2iH1skGbL

dashboard_publisher.py

@@ -172,8 +172,8 @@ def report_to_webapp_dict(report) -> dict:
 
 
 def event_to_dict(ev) -> dict:
-    """EconomicEvent → dict. surprise/minutes_until/is_high_impact are
-    properties, so asdict() would skip them — added explicitly.
+    """EconomicEvent → dict. surprise is a property, so asdict() would
+    skip it — added explicitly.
     actual/forecast/previous stay strings as published ('228K', '0.3%')."""
     return {
         "time": ev.time.astimezone(timezone.utc).isoformat(),
@@ -184,8 +184,6 @@ def event_to_dict(ev) -> dict:
         "previous": ev.previous,
         "actual": ev.actual,
         "surprise": ev.surprise,
-        "minutes_until": _safe_num(ev.minutes_until),
-        "is_high_impact": ev.is_high_impact,
     }