refactor: consolidate duplicated code across web and API packages

- Extract shared render helpers (vacation blocks, range overlay, overbooking blink) into renderHelpers.tsx
- Centralize status badge styles and vacation color maps into status-styles.ts
- Extract dragMath.ts utility from useTimelineDrag for reuse
- Split useInvalidatePlanningViews into useInvalidateTimeline (4 queries) + useInvalidatePlanningViews (8 queries)
- Adopt findUniqueOrThrow() and Prisma select constants across API routers
- Add shared fmtEur() helper for API-side money formatting
- Wrap TimelineResourcePanel and TimelineProjectPanel with React.memo
- Fix pre-existing TS2589 deep type errors in TeamCalendar and VacationModal
- 38 files changed, reducing ~400 lines of duplicated code

Co-Authored-By: claude-flow <ruv@ruv.net>

packages/api/src/router/notification.ts

@@ -1,5 +1,6 @@
 import { z } from "zod";
 import { TRPCError } from "@trpc/server";
+import { findUniqueOrThrow } from "../db/helpers.js";
 import { createTRPCRouter, managerProcedure, protectedProcedure } from "../trpc.js";
 import {
   emitNotificationCreated,
@@ -598,13 +599,10 @@ export const notificationRouter = createTRPCRouter({
   assignTask: managerProcedure
     .input(z.object({ id: z.string(), assigneeId: z.string() }))
     .mutation(async ({ ctx, input }) => {
-      const existing = await ctx.db.notification.findUnique({
-        where: { id: input.id },
-      });
-
-      if (!existing) {
-        throw new TRPCError({ code: "NOT_FOUND", message: "Task not found" });
-      }
+      const existing = await findUniqueOrThrow(
+        ctx.db.notification.findUnique({ where: { id: input.id } }),
+        "Task",
+      );
 
       if (existing.category !== "TASK" && existing.category !== "APPROVAL") {
         throw new TRPCError({