feat: create src/types/candles.ts with Candle interface (task 9.1)

Add shared Candle interface with time, open, high, low, close, and
optional volume fields. Volume is optional because the DB schema does
not store volume but the predict/patterns API routes accept it as an
optional field.

Mark task 9.1 as complete in tasks.md.

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

openspec/changes/code-review-fix/tasks.md

@@ -81,7 +81,7 @@
 
 ## 9. Frontend — Shared Types & Type Safety
 
-- [ ] 9.1 `[sonnet]` Create `src/types/candles.ts` with `Candle` interface
+- [x] 9.1 `[sonnet]` Create `src/types/candles.ts` with `Candle` interface
 - [ ] 9.2 `[sonnet]` Create `src/types/annotations.ts` with `Annotation`, `AnnotationType`, `Geometry` interfaces
 - [ ] 9.3 `[sonnet]` Create `src/types/charts.ts` with `Chart` interface
 - [ ] 9.4 `[sonnet]` Create `src/types/predictions.ts` with `PredictionSpan`, `PredictionState`, `ModelInfo` interfaces

src/types/candles.ts

@@ -0,0 +1,12 @@
+/**
+ * Candle data types for candlestick chart data
+ */
+
+export interface Candle {
+  time: number;
+  open: number;
+  high: number;
+  low: number;
+  close: number;
+  volume?: number;
+}