feat: Add tiptap editor for task descriptions in slide-over panel

- Add updateTask tRPC mutation (name, description fields)
- Replace static description with TiptapEditor in TaskSlideOver
- Auto-detect existing markdown descriptions and convert to tiptap JSON
- Debounced auto-save with flush on close/unmount
- Saving indicator in header

apps/server/trpc/routers/task.ts

@@ -143,6 +143,25 @@ export function taskProcedures(publicProcedure: ProcedureBuilder) {
         return tasks.filter((t) => t.category !== 'detail');
       }),
 
+    updateTask: publicProcedure
+      .input(z.object({
+        id: z.string().min(1),
+        name: z.string().min(1).optional(),
+        description: z.string().nullable().optional(),
+      }))
+      .mutation(async ({ ctx, input }) => {
+        const taskRepository = requireTaskRepository(ctx);
+        const existing = await taskRepository.findById(input.id);
+        if (!existing) {
+          throw new TRPCError({
+            code: 'NOT_FOUND',
+            message: `Task '${input.id}' not found`,
+          });
+        }
+        const { id, ...data } = input;
+        return taskRepository.update(id, data);
+      }),
+
     deleteTask: publicProcedure
       .input(z.object({ id: z.string().min(1) }))
       .mutation(async ({ ctx, input }) => {