Remove JSP and /app/ Prefix

This cleanup step completed the JSP-to-React migration by removing all remaining JSP templates and consolidating the URL structure. Previously, the React SPA was served under `/app/` while legacy JSP pages remained at the root. After full feature parity was achieved, all JSP templates were deleted and the SPA was promoted to serve from the root URL.

Changes

- Removed all JSP template files from the WAR

- Updated SpaRoutingFilter to serve the React SPA from `/` instead of `/app/`

- Redirected legacy `/app/` URLs to root for backwards compatibility

- Cleaned up web.xml servlet and filter mappings for removed JSP servlets

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