Remove @opentelemetry/core peer dependency from @sentry/opentelemetry #21972

Final step of dropping the direct @opentelemetry/core dependency: remove it from @sentry/opentelemetry's peerDependencies once nothing in the package imports it.

Gated on removing the last two direct core imports:

• JS-2820 — SentryPropagator removal (drops W3CBaggagePropagator; the built d.ts must no longer contain extends W3CBaggagePropagator) → this ones done now
• JS-2930 — OTel-resource removal (drops the SDK_INFO import in resource.ts)

Peer removal itself only loosens constraints (not semver-breaking), but it belongs with the v11 messaging.

• Remove @opentelemetry/core from packages/opentelemetry peerDependencies; keep the ^2.6.1 devDependency for the interop tests
• Update packages/opentelemetry/README.md (peer no longer required)
• Verify built types are core-free: rg "@opentelemetry/core" packages/opentelemetry/build — only NOTICE comments may match; build/types/propagator.d.ts must no longer import it
• Verify @sentry/vercel-edge bundle contains no core module
• Scratch check: npm pack, install into a pnpm app WITHOUT @opentelemetry/core, minimal node-core init + one HTTP request (crashes today, must work after)
• v11 migration/changelog entry: peer no longer required (still present transitively via @sentry/node's sdk-trace-base)

Note: this does NOT remove @opentelemetry/core from users' node_modules — it still arrives transitively. Dropping that is the separate SentryTracerProvider track.