feat: add chart annotations

Inline annotation markers on the dashboard chart with create/edit/delete UI.
Color-coded categories: deploy, campaign, incident, other.

lib/api/annotations.ts

@@ -0,0 +1,55 @@
+import apiRequest from './client'
+
+export type AnnotationCategory = 'deploy' | 'campaign' | 'incident' | 'other'
+
+export interface Annotation {
+  id: string
+  site_id: string
+  date: string
+  text: string
+  category: AnnotationCategory
+  created_by: string
+  created_at: string
+  updated_at: string
+}
+
+export interface CreateAnnotationRequest {
+  date: string
+  text: string
+  category?: AnnotationCategory
+}
+
+export interface UpdateAnnotationRequest {
+  date: string
+  text: string
+  category: AnnotationCategory
+}
+
+export async function listAnnotations(siteId: string, startDate?: string, endDate?: string): Promise<Annotation[]> {
+  const params = new URLSearchParams()
+  if (startDate) params.set('start_date', startDate)
+  if (endDate) params.set('end_date', endDate)
+  const qs = params.toString()
+  const res = await apiRequest<{ annotations: Annotation[] }>(`/sites/${siteId}/annotations${qs ? `?${qs}` : ''}`)
+  return res?.annotations ?? []
+}
+
+export async function createAnnotation(siteId: string, data: CreateAnnotationRequest): Promise<Annotation> {
+  return apiRequest<Annotation>(`/sites/${siteId}/annotations`, {
+    method: 'POST',
+    body: JSON.stringify(data),
+  })
+}
+
+export async function updateAnnotation(siteId: string, annotationId: string, data: UpdateAnnotationRequest): Promise<Annotation> {
+  return apiRequest<Annotation>(`/sites/${siteId}/annotations/${annotationId}`, {
+    method: 'PUT',
+    body: JSON.stringify(data),
+  })
+}
+
+export async function deleteAnnotation(siteId: string, annotationId: string): Promise<void> {
+  await apiRequest(`/sites/${siteId}/annotations/${annotationId}`, {
+    method: 'DELETE',
+  })
+}