Updated the INVALID_PREFIX_REGEX to ensure that prefixes starting with a backslash are considered invalid. Previously, only multiple slashes or dot segments were explicitly disallowed at the start.

Also updated the associated validation error message and unit tests to reflect this change.

Updates createRedirectResponse to accept an optional Record<string, string> of headers, allowing custom headers to be merged into the redirect response. The Location and Vary: X-Forwarded-Prefix headers are automatically set to ensure correct routing and proxy behavior.

AngularServerApp now passes relevant headers from the matched route or response context when creating a redirect.

Refactors the `createRedirectResponse` function to use a `Set` for constructing the `Vary` header. This ensures that `X-Forwarded-Prefix` is always present exactly once, and that existing `Vary` values from provided headers are correctly parsed, deduplicated, and preserved.

Updates the associated unit tests to reflect the new header order and verify the deduplication logic.