Resolve #2752: Correct WebSocket room injection and backpressure docs

[ayden94]

Summary

Linked context: #2752 — [audit][area:protocol-adapters] Correct WebSocket room injection and backpressure documentation (priority:p2).

WebSocket room examples injected the type-only WebSocketRoomService contract without a runtime DI token, so the documented pattern failed DI. Cross-runtime room broadcast documentation also promised backpressure behavior that only the Node.js-backed adapter implements.

Changes

• book/intermediate/ch13-websockets.md / .ko.md (Section 13.5): inject WebSocketGatewayLifecycleService via @Inject(...) and type the constructor parameter as WebSocketRoomService; limit backpressure claims to the Node.js-backed adapter and state that fetch-style runtimes do not apply a backpressure policy to room broadcasts. Summary bullet updated to mention the injection token.
• packages/websockets/README.md / .ko.md (Rooms section): same injection token and backpressure runtime limit corrections.
• docs/getting-started/migrate-from-nestjs.md / .ko.md: state the injection token and backpressure runtime limit in the WebSocket migration bullet.
• docs/CONTEXT.md / .ko.md, docs/reference/package-surface.md / .ko.md: mirror the injection token and backpressure runtime limit in discoverability summaries.
• tooling/governance/verify-platform-consistency-governance.mjs: extend the contract companion comment to cover the new WebSocket room injection token and backpressure runtime limit discoverability.
• tooling/governance/websocket-room-injection-backpressure-discoverability.test.ts: regression test asserting the injection token and backpressure runtime limit stay documented across governed English and Korean docs.

Testing

• pnpm docs:sync-check — passed (42 en/ko page pairs, 10 navigation metadata pairs).
• pnpm verify:platform-consistency-governance — passed.
• pnpm exec vitest run tooling/governance/websocket-room-injection-backpressure-discoverability.test.ts — 2 tests passed.
• pnpm exec vitest run tooling/governance/verify-platform-consistency-governance.test.ts — 102 tests passed.
• pnpm exec vitest run packages/websockets/src/public-surface.test.ts — 6 tests passed.

Release impact

• This PR has no consumer-visible release impact.

Docs-only change. No public @fluojs/* package behavior, API surface, package contents, or release metadata changed.

Public export documentation

• Changed public exports include a source-level summary.
• Changed exported functions document matching @param / @returns tags where applicable.
• Source @example blocks and README scenario examples still play complementary roles.

해당 없음 — no public exports under packages/*/src changed.

Behavioral contract

• No documented behavioral contracts were removed without migration notes.
• New behavioral contracts are documented in the affected package README.
• Intentional limitations are explicitly stated (not silently removed).
• Runtime invariants are covered by regression tests.

The corrected room injection token and backpressure runtime limit are now documented as intentional limitations: fetch-style runtimes do not apply a backpressure policy to room broadcasts, and WebSocketRoomService is a type-only contract that must be injected via the lifecycle service token. The regression test in tooling/governance/websocket-room-injection-backpressure-discoverability.test.ts keeps these facts aligned across governed docs.

Platform consistency governance (SSOT)

• SSOT English/Korean mirror structure remains synchronized for changed governance docs.
• If platform contract docs changed, companion updates include discoverability/docs index, tooling or CI enforcement, and regression-test evidence.
• Any package README alignment/conformance claims are backed by the applicable platform harness tests.

pnpm docs:sync-check and pnpm verify:platform-consistency-governance pass. The governance script comment block and the new regression test are the CI/tooling and regression-test companions for this contract-governing doc update.

Closes #2752