task 9.5: create src/types/span-annotations.ts

Add SpanAnnotation, SpanLabelType, and SubSpan interfaces extracted from
duplicate inline definitions across SpanAnnotationManager, SpanAnnotationList,
SpanPopover, Toolbox, and page.tsx components.

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

src/types/span-annotations.ts

@@ -0,0 +1,50 @@
+/**
+ * Span annotation types for chart pattern labeling
+ */
+
+/**
+ * A sub-span represents a nested time range within a parent span annotation,
+ * used to mark sub-structures or phases within a larger pattern.
+ */
+export interface SubSpan {
+  start_time: number;
+  end_time: number;
+  label: string;
+  color?: string;
+  notes?: string | null;
+}
+
+/**
+ * A span annotation marks a time range on a chart with a pattern label
+ * and optional metadata such as confidence, outcome, and notes.
+ */
+export interface SpanAnnotation {
+  id: number;
+  chart_id: number;
+  start_time: number;
+  end_time: number;
+  label: string;
+  confidence: number | null;
+  outcome: string | null;
+  notes: string | null;
+  sub_spans: SubSpan[] | null;
+  color: string;
+  source?: string;
+  model_prediction?: Record<string, unknown> | null;
+  created_at: number;
+}
+
+/**
+ * A span label type defines a named pattern category that can be applied
+ * to span annotations, with display metadata and optional keyboard shortcut.
+ */
+export interface SpanLabelType {
+  id: number;
+  name: string;
+  display_name: string;
+  color: string;
+  hotkey: string | null;
+  is_active: boolean;
+  sort_order: number;
+  created_at: number;
+}