feat(tanstackstart-react): Add server-side route parametrization (#21147)

Server transactions now use parametrized route names instead of raw
URLs. `GET /users/123` becomes `GET /users/$id`, fixing high-cardinality
transaction grouping.

The framework provides no way to do this natively, so this is
implemented using a build manifest approach that should hopefully work
in most cases. Route patterns are extracted from `routeTree.gen.ts` at
build time and presorted by number of static/dynamic segments, then
matched against request URLs at runtime in `wrapFetchWithSentry`.

Closes https://github.com/getsentry/sentry-javascript/issues/18284

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Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>