fix(elysia): Use node transport by default on Node.js

[sx4im]

init() in the Elysia SDK unconditionally defaulted to Bun's fetch transport, even when running on Node.js. That silently replaced the node transport, losing proxy support (http_proxy/HTTPS_PROXY), custom CA handling via NODE_EXTRA_CA_CERTS, and keep-alive agent tuning for anyone running Elysia on Node behind a corporate proxy.

This picks the default transport by detected runtime, the same way getRuntime() already detects it: makeFetchTransport on Bun, makeNodeTransport everywhere else. An explicitly provided transport option is still respected, and no dependency structure changes — @sentry/bun already re-exports makeNodeTransport from @sentry/node.

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Fixes #24048

Notes on verification: yarn test in packages/elysia passes (33/33, including a new regression test that failed before the fix). yarn lint reports 8 errors in the package, all pre-existing on the untouched tree (unbuilt @sentry/bun types in this environment; the change removes one of them and adds none). A full yarn build:dev is blocked by a pre-existing server-utils types failure from vite version drift, unrelated to this change; the elysia transpile build succeeds.