Add economic calendar module to filter trades near high-impact events

Introduces a full Trading Economics API pipeline that fetches, stores, and
queries economic events (NFP, CPI, rate decisions, etc.) so the backtester
can block trade entries within a configurable buffer window of high-impact
releases — reducing slippage and false signals.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

sql/create_economic_calendar.sql

@@ -0,0 +1,20 @@
+CREATE TABLE economic_calendar (
+    event_datetime   TIMESTAMPTZ       NOT NULL,
+    country          TEXT              NOT NULL,
+    event_name       TEXT              NOT NULL,
+    currency         TEXT,
+    impact           TEXT,
+    impact_numeric   INTEGER,
+    actual           DOUBLE PRECISION,
+    forecast         DOUBLE PRECISION,
+    previous         DOUBLE PRECISION,
+    revised          DOUBLE PRECISION,
+    reference        TEXT,
+    source           TEXT,
+    last_updated     TIMESTAMPTZ       DEFAULT now(),
+    PRIMARY KEY (event_datetime, country, event_name)
+);
+
+CREATE INDEX idx_ec_datetime  ON economic_calendar (event_datetime DESC);
+CREATE INDEX idx_ec_currency  ON economic_calendar (currency);
+CREATE INDEX idx_ec_impact    ON economic_calendar (impact_numeric);