feat: add Filament admin panel with migrations and design spec

- Add AdminPanelProvider mounting panel at `/admin` with `is_admin` auth guard
- Add `is_admin` boolean column to users table
- Add brent_prices and price_predictions tables with appropriate indexes
- Add comprehensive admin design spec covering resources, dashboard, navigation, and build order
- Configure default panel with amber primary color and standard middleware stack
- Add compiled Filament assets (actions.js, app.css)

.claude/rules/database.md

@@ -91,6 +91,31 @@ INDEX (user_id, expires_at)
 ```
 OTP codes expire after 10 minutes. Mark `used_at` on success — never delete rows.
 
+### brent_prices (daily Brent crude from FRED)
+```
+date            DATE PRIMARY KEY   — trading day (no weekends/holidays)
+price_usd       DECIMAL(8,2)       — spot price USD per barrel
+```
+Populated daily by `OilPriceService::fetchBrentPrices()` via FRED API.
+FRED returns `"."` for non-trading days — these are filtered out before insert.
+Upserted on refetch so duplicate dates never occur.
+
+### price_predictions (oil price direction forecast)
+```
+id              BIGINT UNSIGNED AUTO_INCREMENT
+predicted_for   DATE               — the date this prediction covers
+source          ENUM('llm','ewma') — which method generated it
+direction       ENUM('rising','falling','flat')
+confidence      TINYINT            — 0–100 (LLM max 85, EWMA max 65)
+reasoning       TEXT NULLABLE      — plain-English explanation
+generated_at    DATETIME
+
+INDEX (predicted_for, source)
+```
+Generated daily by `OilPriceService::generatePrediction()`.
+LLM (Anthropic) is tried first; EWMA is used as fallback if LLM fails or key not set.
+Signal 4 in AlertScoringService reads from this table — never from brent_prices directly.
+
 ## Supermarket brands (StationTaggingService)
 
 Match station `name` (case-insensitive) against: