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/components/CreateTaskModal.tsx

@@ -12,6 +12,7 @@ interface CreateTaskModalProps {
     priority?: string;
     projectId?: string;
     dueDate?: string;
+    estimatedHours?: number;
   }) => void;
 }
 
@@ -22,6 +23,7 @@ export function CreateTaskModal({ open, onClose, onCreate }: CreateTaskModalProp
   const [priority, setPriority] = useState("medium");
   const [projectId, setProjectId] = useState("");
   const [dueDate, setDueDate] = useState("");
+  const [estimatedHours, setEstimatedHours] = useState("");
   const [projects, setProjects] = useState<Project[]>([]);
   const [showAdvanced, setShowAdvanced] = useState(false);
 
@@ -53,6 +55,7 @@ export function CreateTaskModal({ open, onClose, onCreate }: CreateTaskModalProp
       priority,
       projectId: projectId || undefined,
       dueDate: dueDate ? new Date(dueDate).toISOString() : undefined,
+      estimatedHours: estimatedHours ? Number(estimatedHours) : undefined,
     });
     // Reset form
     setTitle("");
@@ -61,6 +64,7 @@ export function CreateTaskModal({ open, onClose, onCreate }: CreateTaskModalProp
     setPriority("medium");
     setProjectId("");
     setDueDate("");
+    setEstimatedHours("");
     setShowAdvanced(false);
     onClose();
   };
@@ -179,6 +183,23 @@ export function CreateTaskModal({ open, onClose, onCreate }: CreateTaskModalProp
                 </div>
               </div>
 
+              {/* Estimated Hours */}
+              <div>
+                <label className="text-xs font-medium text-gray-500 block mb-1">Estimated Hours</label>
+                <div className="flex items-center gap-2">
+                  <input
+                    type="number"
+                    min="0"
+                    step="1"
+                    value={estimatedHours}
+                    onChange={(e) => setEstimatedHours(e.target.value)}
+                    placeholder="0"
+                    className="w-24 text-sm border border-gray-200 rounded-lg px-3 py-1.5 focus:outline-none focus:ring-2 focus:ring-amber-400 bg-white"
+                  />
+                  <span className="text-sm text-gray-500">hours</span>
+                </div>
+              </div>
+
               {/* Source */}
               <div>
                 <label className="text-xs font-medium text-gray-500 block mb-1">Source</label>