Add 404 pages

[andreaskienle]

Fixes openmcp-project/backlog#164

This PR makes the following changes to user experience:

• Invalid paths (e.g. http://localhost:5173/#/mcp/INVALID_PATH) are now redirected to home (/) – previously users were stuck on an empty screen
• Pages for non-existing projects (or projects where the user has no authorization) (e.g. http://localhost:5173/#/mcp/projects/NON_EXISTING_PROJECT) will now show a proper 404 message – previously users were stuck on a "Loading" screen:
  
• Same is true for non-existing MCPs (e.g. http://localhost:5173/#/mcp/projects/webapp-playground/workspaces/development/mcps/NON_EXISTING_MCP/context/context):
  

[Copilot]

Pull Request Overview

This PR implements proper 404 error handling by replacing the previous ControlPlaneListView with a new ProjectPage component and updating the McpPage to handle non-existing resources. The changes redirect users from invalid paths to the home page and show proper 404 messages instead of leaving users stuck on loading screens.

• Adds 404 error detection and handling for projects and MCPs
• Creates a reusable NotFoundBanner component for consistent error messaging
• Implements proper loading states and error boundaries for better UX

Reviewed Changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
src/views/ControlPlanes/ControlPlaneListView.tsx	Completely removed - functionality moved to ProjectPage
src/spaces/onboarding/pages/ProjectPage.tsx	New page component with proper error handling for projects
src/spaces/mcp/pages/McpPage.tsx	Enhanced with 404 detection and loading states
src/lib/api/types/crate/listWorkspaces.ts	Made projectName parameter optional
src/lib/api/types/crate/controlPlanes.ts	Made parameters optional for better error handling
src/lib/api/error.ts	Added utility function to detect 404/403 errors
src/components/Ui/NotFoundBanner/NotFoundBanner.tsx	New reusable 404 banner component
src/components/Ui/IllustratedBanner/IllustratedBanner.tsx	Enhanced to support React nodes as subtitles
src/components/ControlPlanes/List/ControlPlaneListAllWorkspaces.tsx	Refactored to accept workspaces as props
src/AppRouter.tsx	Updated routes and added catch-all redirect