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/[id]/route.ts

@@ -0,0 +1,87 @@
+import { NextRequest, NextResponse } from 'next/server';
+import { db } from '@/lib/db';
+import { spanAnnotations } from '@/lib/db/schema';
+import { eq } from 'drizzle-orm';
+
+// PATCH - Update span annotation
+export async function PATCH(
+  request: NextRequest,
+  { params }: { params: Promise<{ id: string }> }
+) {
+  try {
+    const { id } = await params;
+    const body = await request.json();
+
+    const { label, confidence, outcome, notes, sub_spans } = body;
+
+    // Check if the span exists
+    const existing = await db
+      .select()
+      .from(spanAnnotations)
+      .where(eq(spanAnnotations.id, parseInt(id)))
+      .limit(1);
+
+    if (existing.length === 0) {
+      return NextResponse.json(
+        { error: 'Span annotation not found' },
+        { status: 404 }
+      );
+    }
+
+    // Build update object with only provided fields
+    const updates: any = {};
+    if (label !== undefined) updates.label = label;
+    if (confidence !== undefined) updates.confidence = confidence;
+    if (outcome !== undefined) updates.outcome = outcome;
+    if (notes !== undefined) updates.notes = notes;
+    if (sub_spans !== undefined) updates.sub_spans = sub_spans ? JSON.stringify(sub_spans) : null;
+
+    const result = await db
+      .update(spanAnnotations)
+      .set(updates)
+      .where(eq(spanAnnotations.id, parseInt(id)))
+      .returning();
+
+    return NextResponse.json(result[0]);
+  } catch (error: any) {
+    console.error('Error updating span annotation:', error);
+    return NextResponse.json(
+      { error: 'Failed to update span annotation' },
+      { status: 500 }
+    );
+  }
+}
+
+// DELETE - Delete span annotation
+export async function DELETE(
+  request: NextRequest,
+  { params }: { params: Promise<{ id: string }> }
+) {
+  try {
+    const { id } = await params;
+
+    // Check if the span exists
+    const existing = await db
+      .select()
+      .from(spanAnnotations)
+      .where(eq(spanAnnotations.id, parseInt(id)))
+      .limit(1);
+
+    if (existing.length === 0) {
+      return NextResponse.json(
+        { error: 'Span annotation not found' },
+        { status: 404 }
+      );
+    }
+
+    await db.delete(spanAnnotations).where(eq(spanAnnotations.id, parseInt(id)));
+
+    return NextResponse.json({ message: 'Span annotation deleted successfully' });
+  } catch (error) {
+    console.error('Error deleting span annotation:', error);
+    return NextResponse.json(
+      { error: 'Failed to delete span annotation' },
+      { status: 500 }
+    );
+  }
+}