feat(forward): add realtime conversations and history

[moonyue-w]

Summary

Add Forward Realtime Beta Conversation creation, authenticated Node.js WebSocket connections and persisted History with independent before pagination. Connections expose text/PCM16 input, typed and unknown events, Work progress, playback receipts, interruption and acknowledged graceful closure.

Why

The TypeScript SDK cannot currently use Forward's Realtime API. This adds the public creation/connection/history surface while reusing the existing authentication and HTTP resource conventions. The Node transport loads only when connecting so existing browser HTTP imports remain usable.

Verification

• npm run build
• npm run typecheck
• npm test
• npm run docs:check
• Relevant examples run or import successfully (--help smoke checks)
• Account-backed integration tests run

After merging the latest main: 3676 offline tests passed, 0 skipped; 59 focused Realtime checks. Package checks covered Node 20.12, CJS/ESM, HTTP/browser imports, public types and a local WebSocket connection from an installed tarball. Changelog/release-notes checks passed.

CN/Global × PAT/Forward-bound SAT: 4 text and 4 PCM scenarios passed through npm run test:live:realtime. These verify creation, ready, ping/pong, nonempty transcripts, decoded output audio, matching close acknowledgements and filtered History pagination. Temporary test Identities were cleaned up; existing Templates were preserved. Conversation IDs are retained because there is no public delete API. Audio devices were not tested.

Additional live Work checks observed accepted/running/completed and persisted announcements. The first matrix had 3 passes and a Global PAT History assertion failure. That single unchanged case passed on rerun after adding diagnostic detail; the initial cause remains undetermined and is not represented as a fixed SDK bug. Offline tests also cover receive handoff, iteration without connection closure, protocol validation, cancellation, redirects and bounded queues.

Impact

• Public API or behavior changed
• User-facing changes added to CHANGELOG.md under Unreleased
• CommonJS, ESM, and subpath exports remain valid
• Generated API documentation updated
• Contract or wire-field fixtures updated
• Go and Python parity considered
• Migration notes added for a breaking change
• No credentials, .env.live, logs, or generated test output committed

This is additive; migration notes are not required. Adds ws and its development types while retaining Node >=20.12. Realtime connections are Node-only. Stage deadlines are separate from HTTP request timeouts; connections do not automatically reconnect or replay input. Playback receipts remain application-owned.

Realtime SA access currently requires a Forward-issued bound SAT. The platform ServiceAccountCredential exchange does not create that binding; its SAT returned 403 during the initial live checks. Passing a Forward-issued SAT through the existing direct-token interface passed. The SAT issuance API is already merged into main (#16); this PR builds on it and does not change platform credential renewal. Template Realtime configuration APIs are outside this PR.