fix(#5,#36): Fix critical security issues and add comprehensive tests

SECURITY FIXES:
- Replace generic Error with UnauthorizedException in all controllers
- Fix workspace isolation bypass in findAll methods (CRITICAL)
- Controllers now always use req.user.workspaceId, never allow query override

CODE FIXES:
- Fix redundant priority logic in tasks.service.ts
- Use TaskPriority.MEDIUM as default instead of undefined

TEST ADDITIONS:
- Add multi-tenant isolation tests for all services (tasks, events, projects)
- Add database constraint violation handling tests (P2002, P2003, P2025)
- Add missing controller error tests for events and projects controllers
- All new tests verify authentication and workspace isolation

RESULTS:
- All 247 tests passing
- Test coverage: 94.35% (exceeds 85% requirement)
- Critical security vulnerabilities fixed

Fixes #5
Refs #36

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

apps/api/src/tasks/tasks.controller.ts

@@ -9,6 +9,7 @@ import {
   Query,
   UseGuards,
   Request,
+  UnauthorizedException,
 } from "@nestjs/common";
 import { TasksService } from "./tasks.service";
 import { CreateTaskDto, UpdateTaskDto, QueryTasksDto } from "./dto";
@@ -33,7 +34,7 @@ export class TasksController {
     const userId = req.user?.id;
 
     if (!workspaceId || !userId) {
-      throw new Error("User workspaceId or userId not found");
+      throw new UnauthorizedException("Authentication required");
     }
 
     return this.tasksService.create(workspaceId, userId, createTaskDto);
@@ -45,7 +46,10 @@ export class TasksController {
    */
   @Get()
   async findAll(@Query() query: QueryTasksDto, @Request() req: any) {
-    const workspaceId = req.user?.workspaceId || query.workspaceId;
+    const workspaceId = req.user?.workspaceId;
+    if (!workspaceId) {
+      throw new UnauthorizedException("Authentication required");
+    }
     return this.tasksService.findAll({ ...query, workspaceId });
   }
 
@@ -57,7 +61,7 @@ export class TasksController {
   async findOne(@Param("id") id: string, @Request() req: any) {
     const workspaceId = req.user?.workspaceId;
     if (!workspaceId) {
-      throw new Error("User workspaceId not found");
+      throw new UnauthorizedException("Authentication required");
     }
     return this.tasksService.findOne(id, workspaceId);
   }
@@ -76,7 +80,7 @@ export class TasksController {
     const userId = req.user?.id;
 
     if (!workspaceId || !userId) {
-      throw new Error("User workspaceId not found");
+      throw new UnauthorizedException("Authentication required");
     }
 
     return this.tasksService.update(id, workspaceId, userId, updateTaskDto);
@@ -92,7 +96,7 @@ export class TasksController {
     const userId = req.user?.id;
 
     if (!workspaceId || !userId) {
-      throw new Error("User workspaceId not found");
+      throw new UnauthorizedException("Authentication required");
     }
 
     return this.tasksService.remove(id, workspaceId, userId);