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

test_all.py

@@ -755,13 +755,6 @@ def _():
     assert quote == "USD"
 
 
-@test("NewsEngine._parse_pair with =X suffix")
-def _():
-    base, quote = NewsEngine._parse_pair("EURUSD=X")
-    assert base == "EUR"
-    assert quote == "USD"
-
-
 @test("NewsEngine._parse_pair for XAU pair")
 def _():
     base, quote = NewsEngine._parse_pair("XAU/USD")
@@ -3597,7 +3590,11 @@ def _():
     provider = providers.oanda.OandaDataProvider.__new__(
         providers.oanda.OandaDataProvider)
     assert provider._to_oanda_instrument("XAU/USD") == "XAU_USD"
-    assert provider._to_oanda_instrument("EUR/USD") == "EUR_USD"
+    try:
+        provider._to_oanda_instrument("EUR/USD")
+        assert False, "unregistered symbol must raise, not be guessed"
+    except DataIntegrityError:
+        pass
 
 
 @test("providers.oanda: granularity mapping covers all scan timeframes")
@@ -5151,8 +5148,7 @@ def _():
     assert d["event"] == "Non-Farm Payrolls"
     assert d["actual"] == "228K"            # strings stay strings
     assert d["surprise"] == "positive"      # property, added explicitly
-    assert d["is_high_impact"] is True
-    assert isinstance(d["minutes_until"], float)
+    assert "minutes_until" not in d           # frozen-at-publish value, dropped
     assert d["time"] == "2026-08-07T12:30:00+00:00"
     json.dumps(d, allow_nan=False)