Add backlog audit and task update command

- agents/prompts/backlog_audit.md: QA analyst prompt for checking
  which pending tasks are already implemented in the codebase
- agents/runner.py: run_audit() — project-level agent that reads
  all pending tasks, inspects code, returns classification
- cli/main.py: kin audit <project_id> — runs audit, offers to mark
  done tasks; kin task update <id> --status --priority
- web/api.py: POST /api/projects/{id}/audit (runs audit inline),
  POST /api/projects/{id}/audit/apply (batch mark as done)
- Frontend: "Audit backlog" button on ProjectView with results
  modal showing already_done/still_pending/unclear categories

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

web/frontend/src/api.ts

@@ -108,6 +108,21 @@ export interface CostEntry {
   total_duration_seconds: number
 }
 
+export interface AuditItem {
+  id: string
+  reason: string
+}
+
+export interface AuditResult {
+  success: boolean
+  already_done: AuditItem[]
+  still_pending: AuditItem[]
+  unclear: AuditItem[]
+  duration_seconds?: number
+  cost_usd?: number
+  error?: string
+}
+
 export const api = {
   projects: () => get<Project[]>('/projects'),
   project: (id: string) => get<ProjectDetail>(`/projects/${id}`),
@@ -129,4 +144,8 @@ export const api = {
     post<{ status: string }>(`/tasks/${id}/run`, { allow_write: allowWrite }),
   bootstrap: (data: { path: string; id: string; name: string }) =>
     post<{ project: Project }>('/bootstrap', data),
+  auditProject: (projectId: string) =>
+    post<AuditResult>(`/projects/${projectId}/audit`, {}),
+  auditApply: (projectId: string, taskIds: string[]) =>
+    post<{ updated: string[]; count: number }>(`/projects/${projectId}/audit/apply`, { task_ids: taskIds }),
 }