docs(openspec): add reporting API contract documentation

Add comprehensive API documentation for the reporting endpoint:
- Request/response structure
- View type inference (did/is/will)
- Blank vs explicit zero semantics
- Status values and error responses

Related to enhanced-allocation change.

frontend/src/lib/services/allocationService.ts

@@ -9,9 +9,10 @@ import { api } from './api';
 export interface Allocation {
   id: string;
   project_id: string;
-  team_member_id: string;
+  team_member_id: string | null;
   month: string;
   allocated_hours: string;
+  allocation_indicator?: 'green' | 'yellow' | 'red' | 'gray';
   created_at: string;
   updated_at: string;
   project?: {
@@ -22,7 +23,7 @@ export interface Allocation {
   team_member?: {
     id: string;
     name: string;
-  };
+  } | null;
 }
 
 export interface CreateAllocationRequest {

frontend/src/lib/services/projectMonthPlanService.ts

@@ -0,0 +1,53 @@
+import { api } from '$lib/services/api';
+
+export interface ProjectMonthPlan {
+  project_id: string;
+  project_name: string;
+  approved_estimate: number;
+  months: Record<string, {
+    id: string;
+    planned_hours: number | null;
+    is_blank: boolean;
+  } | null>;
+  plan_sum: number;
+  reconciliation_status: 'OVER' | 'UNDER' | 'MATCH';
+}
+
+export interface ProjectMonthPlansResponse {
+  data: ProjectMonthPlan[];
+  meta: {
+    year: number;
+  };
+}
+
+export interface BulkUpdateRequest {
+  year: number;
+  items: Array<{
+    project_id: string;
+    month: string;
+    planned_hours: number | null;
+  }>;
+}
+
+export interface BulkUpdateResponse {
+  message: string;
+  summary: {
+    created: number;
+    updated: number;
+    cleared: number;
+  };
+}
+
+class ProjectMonthPlanService {
+  async getPlans(year: number): Promise<ProjectMonthPlansResponse> {
+    const response = await api.get<ProjectMonthPlansResponse>(`/project-month-plans?year=${year}`);
+    return response.data;
+  }
+
+  async bulkUpdate(request: BulkUpdateRequest): Promise<BulkUpdateResponse> {
+    const response = await api.put<BulkUpdateResponse>('/project-month-plans/bulk', request);
+    return response.data;
+  }
+}
+
+export const projectMonthPlanService = new ProjectMonthPlanService();