feat: task time estimates and velocity chart on dashboard

- Added estimatedHours column to tasks schema
- Backend: create/update support for estimatedHours
- New /api/tasks/stats/velocity endpoint: daily completions, weekly velocity, estimate totals
- Dashboard: velocity chart with 7-day bar chart, this week count, avg/week, estimate summary
- TaskDetailPanel: estimated hours input field
- CreateTaskModal: estimated hours in advanced options
- TaskCard, KanbanBoard, TaskPage: estimate badge display

frontend/src/lib/api.ts

@@ -1,4 +1,4 @@
-import type { Task, Project, ProjectWithTasks } from "./types";
+import type { Task, Project, ProjectWithTasks, VelocityStats } from "./types";
 
 const BASE = "/api/tasks";
 
@@ -38,7 +38,7 @@ export async function reorderTasks(ids: string[], token?: string): Promise<void>
 }
 
 export async function createTask(
-  task: { title: string; description?: string; source?: string; priority?: string; status?: string; projectId?: string; dueDate?: string },
+  task: { title: string; description?: string; source?: string; priority?: string; status?: string; projectId?: string; dueDate?: string; estimatedHours?: number },
   token?: string
 ): Promise<Task> {
   const headers: Record<string, string> = { "Content-Type": "application/json" };
@@ -64,6 +64,14 @@ export async function deleteTask(id: string, token?: string): Promise<void> {
   if (!res.ok) throw new Error("Failed to delete task");
 }
 
+// ─── Velocity Stats ───
+
+export async function fetchVelocityStats(): Promise<VelocityStats> {
+  const res = await fetch(`${BASE}/stats/velocity`, { credentials: "include" });
+  if (!res.ok) throw new Error("Failed to fetch velocity stats");
+  return res.json();
+}
+
 // ─── Projects API ───
 
 const PROJECTS_BASE = "/api/projects";