[Automated][tcgc] Document versionsEnum, SSE/stream metadata, and boolean string encoding

[github-actions]

Summary

Incremental TCGC documentation update based on source changes since the last run. All updates are in the emitter developer guideline (guideline.md), which is the correct audience for these type-graph additions.

Changes to emitter developer docs (guideline.md)

• SdkClientType.versionsEnum — documented the new field in the Client section. It is the SdkEnumType holding the service's API versions (same object as in SdkPackage.enums, ApiVersionEnum usage). Undefined for unversioned services and multi-service root clients; single-service sub clients still expose their own.
• SSE / stream metadata — added a Streaming and server-sent events subsection under Operation, documenting SdkStreamMetadata (streamMetadata) and the new SdkSseMetadata / SdkSseEventMetadata (sseMetadata, present only for SSEStream/text/event-stream), including all SdkSseEventMetadata fields (eventType, isTerminalEvent, isEventEnvelope, type/payloadType, content types).
• boolean @encode(string) — updated the Built-in Types bullet to note that boolean (in addition to integer kinds) now supports @encode(string), producing encode: "string".

Knowledge base

• Recorded lessons for the above features, plus a note that the no-unnamed-types linter rule was added then removed in the same commit batch (net: not an active rule; active rules remain require-client-suffix, property-name-conflict, csharp-no-url-suffix).

Metadata

• Updated tcgc.meta.json to record the checkout commit for the next incremental run.

Notes

• No <ClientTabs> examples were added — these features are emitter-consumed type-graph metadata documented in the guideline, not new user-facing spec-authoring patterns.
• No Spector specs were added — the changes are type-graph metadata / encoding behavior covered by existing unit tests (versioning.test.ts, sse.test.ts, streams.test.ts, built-in.test.ts), not new wire-level behaviors.

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