feat(solid-2): add @sentry/solid-2 — Solid 2 SDK (client + server)

[ryansolid]

A Sentry SDK for Solid 2 (solid-js ^2.0.0-rc.9). One package covers every Solid 2 project — client and server, any router, any host — because Solid 2 moved the things an SDK needs into the runtime itself. There is no SolidStart for Solid 2 and there is nothing in this package for a router or a host: the runtime has error hooks on both platforms, a structured observability channel (OBSERVE.records), an attribution engine that names the user interaction and the route behind every write (routers declare navigations to it with withOrigin; the SDK never sees router code), and a server-side trace-context slot whose answer the runtime carries to the browser on its own (Server-Timing, the <meta> pair). So where @sentry/solid plus @sentry/solidstart needed a router integration, a middleware to rewrite HTML, and a --import preload per host, this is one init() on each side that subscribes.

The server half's one requirement is @sentry/node's, not Solid's: init() must run before the app's server graph loads so OpenTelemetry can patch node:http and friends. Each host does that its own way — node --import, a first import in a CJS entry; for apps served by @solidjs/vite-plugin's handler, its start.instrument option is that preload, since ESM hoisting defeats "import it first" there. The unit tests run the server integrations against bare renderToStream with no plugin involved; the e2e app is a plugin-hosted app because that is the reference deployment and it exercises start.instrument.

Errors report in every Solid build tier through the two hooks, once per error object, with where it was thrown and where it was met. Tracing is opt-in and needs Solid's observe build (the observe export condition plus the compiler's componentNames; solid({ observe: true }) sets both): one root span per user interaction with its navigations, holds and server-function calls as children (joined by the engine's object identity, not by time); server-function executions and waiting <Loading> boundaries as spans under OTel's http.server; the browser pageload continuing the server trace with no middleware.

Decisions worth a look: records set span status only and never capture — the same error reaches a hook, and Sentry's once-per-object guard made whichever ran first win (the e2e app caught the record misreporting a handled boundary catch as an unhandled crash). Element text from interaction targets is stripped unless targetText: true. A call that lands after its interaction settled (onClick={async () => set(await call())}) is parented under the ended interaction span, marked after_settle. Interactions are root spans rather than children of the pageload idle span; open to changing that.

The package name is a working one — @sentry/solid-2 vs. a new major of @sentry/solid still needs a decision, and nothing in the code depends on it.

docs/solid-2-observe.md is the reviewer's brief on what the runtime exposes. The e2e app is marked optional until the CI matrix has run it.