feat: add database schema, migrations, and API endpoints for span annotations

- Add span_label_types and span_annotations tables to schema
- Seed default span label types (bull_flag, bear_flag, etc.)
- Implement CRUD API endpoints for span label types
- Implement CRUD API endpoints for span annotations
- Add time swap validation in POST endpoint (start_time <= end_time)

src/app/api/span-annotations/route.ts

@@ -0,0 +1,86 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { db } from '@/lib/db';
+import { spanAnnotations } from '@/lib/db/schema';
+import { eq, desc } from 'drizzle-orm';
+
+// GET - List all span annotations for a chart
+export async function GET(request: NextRequest) {
+  try {
+    const { searchParams } = request.nextUrl;
+    const chartId = searchParams.get('chartId');
+
+    if (!chartId) {
+      return NextResponse.json(
+        { error: 'chartId parameter is required' },
+        { status: 400 }
+      );
+    }
+
+    const spans = await db
+      .select()
+      .from(spanAnnotations)
+      .where(eq(spanAnnotations.chart_id, parseInt(chartId)))
+      .orderBy(desc(spanAnnotations.start_time));
+
+    return NextResponse.json(spans);
+  } catch (error) {
+    console.error('Error fetching span annotations:', error);
+    return NextResponse.json(
+      { error: 'Failed to fetch span annotations' },
+      { status: 500 }
+    );
+  }
+}
+
+// POST - Create new span annotation
+export async function POST(request: NextRequest) {
+  try {
+    const body = await request.json();
+    const {
+      chart_id,
+      start_time,
+      end_time,
+      label,
+      confidence,
+      outcome,
+      notes,
+      sub_spans,
+      color,
+    } = body;
+
+    if (!chart_id || start_time === undefined || end_time === undefined || !label) {
+      return NextResponse.json(
+        { error: 'chart_id, start_time, end_time, and label are required' },
+        { status: 400 }
+      );
+    }
+
+    // Ensure start_time <= end_time (swap if needed)
+    const actualStartTime = Math.min(start_time, end_time);
+    const actualEndTime = Math.max(start_time, end_time);
+
+    const result = await db
+      .insert(spanAnnotations)
+      .values({
+        chart_id,
+        start_time: actualStartTime,
+        end_time: actualEndTime,
+        label,
+        confidence: confidence || null,
+        outcome: outcome || null,
+        notes: notes || null,
+        sub_spans: sub_spans ? JSON.stringify(sub_spans) : null,
+        color: color || '#2196F3',
+        created_at: Math.floor(Date.now() / 1000),
+      })
+      .returning();
+
+    return NextResponse.json(result[0], { status: 201 });
+  } catch (error: any) {
+    console.error('Error creating span annotation:', error);
+    return NextResponse.json(
+      { error: 'Failed to create span annotation' },
+      { status: 500 }
+    );
+  }
+}