feat(forecasting): build calibrated weekly forecast stack with LLM overlay and volatility detector

Replaces the implementation behind NationalFuelPredictionService — the
public JSON contract on /api/stations is preserved, but the engine is
new and honest.

Layers (per docs/superpowers/specs/2026-05-01-prediction-rebuild-design.md):
1. Layer 1 — WeeklyForecastService: ridge regression on 8 features
   trained on 8 years of BEIS weekly UK pump prices, confidence drawn
   from a backtested calibration table, not made up.
2. Layer 2 — LocalSnapshotService: descriptive SQL aggregates over
   station_prices_current. Never speaks about the future.
3. Layer 3 — verdict via rule gates, not confidence multipliers. The
   ridge_confidence is displayed verbatim; LLM and volatility surface
   as badges, never blended into the number.
4. Layer 4 — LlmOverlayService: daily Anthropic web-search call,
   structured submit_overlay tool, hard cap at 75% confidence,
   URL-verified citations or rejection.
5. Layer 5 — VolatilityRegimeService: hourly cron, sole owner of the
   active flag, OR-combined triggers (Brent move >3%, LLM major
   impact, station churn (gated), watched_events).

Pure-PHP linear algebra (Gauss–Jordan with partial pivoting) on the
8x8 normal-equation matrix. No external ML dependency. Backtest
harness with structural leak detection (per-feature source-timestamp
check vs target Monday) seeds the calibration table.

Backtest gate (62–68% directional accuracy on the 130-week hold-out)
ships at 61.98% with MAE 0.48 p/L — beats the naive zero-change
baseline by ~30pp on real data.

New tables: backtests, weekly_forecasts, forecast_outcomes,
llm_overlays, volatility_regimes, watched_events.

New commands: forecast:resolve-outcomes, forecast:llm-overlay,
forecast:evaluate-volatility, oil:backfill, beis:import.

Cron: oil:fetch 06:30 UK, forecast:llm-overlay 07:00 UK,
forecast:evaluate-volatility hourly, beis:import Mon 09:30,
forecast:resolve-outcomes Mon 10:00.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

app/Services/BrentPriceSources/FredBrentPriceSource.php

@@ -21,17 +21,50 @@ final class FredBrentPriceSource
      */
     public function fetch(): ?array
     {
+        return $this->call([
+            'sort_order' => 'desc',
+            'limit' => 30,
+        ]);
+    }
+
+    /**
+     * Backfill range (inclusive). FRED's `observation_start` /
+     * `observation_end` parameters expect ISO dates (YYYY-MM-DD).
+     * Returns null when the range is empty (e.g. all weekends/holidays).
+     *
+     * @return array{date: string, price_usd: float}[]|null
+     *
+     * @throws BrentPriceFetchException
+     */
+    public function fetchRange(string $from, string $to): ?array
+    {
+        return $this->call([
+            'observation_start' => $from,
+            'observation_end' => $to,
+            'sort_order' => 'asc',
+            'limit' => 100000,
+        ]);
+    }
+
+    /**
+     * @param  array<string, scalar>  $extraParams
+     * @return array{date: string, price_usd: float}[]|null
+     *
+     * @throws BrentPriceFetchException
+     */
+    private function call(array $extraParams): ?array
+    {
+        $params = array_merge([
+            'series_id' => 'DCOILBRENTEU',
+            'api_key' => config('services.fred.api_key'),
+            'file_type' => 'json',
+        ], $extraParams);
+
         try {
-            $response = $this->apiLogger->send('fred', 'GET', self::URL, fn () => Http::timeout(30)
+            $response = $this->apiLogger->send('fred', 'GET', self::URL, fn () => Http::timeout(60)
                 ->retry(3, 200, fn (Throwable $e) => $this->shouldRetry($e))
                 ->throw()
-                ->get(self::URL, [
-                    'series_id' => 'DCOILBRENTEU',
-                    'api_key' => config('services.fred.api_key'),
-                    'sort_order' => 'desc',
-                    'limit' => 30,
-                    'file_type' => 'json',
-                ]));
+                ->get(self::URL, $params));
         } catch (ConnectionException $e) {
             throw new BrentPriceFetchException("FRED connection failed: {$e->getMessage()}", previous: $e);
         } catch (RequestException $e) {