[Automated][tcgc] Document SSE metadata, versionsEnum, and boolean string encoding in TCGC emitter docs

[github-actions]

Summary

Incremental documentation update for @azure-tools/typespec-client-generator-core (TCGC) based on recent source changes to the client type graph. Updates the emitter developer guideline and the doc-updater knowledge base.

Changes

Emitter developer docs (guideline.md):

• Server-Sent Events / streaming — added a "Streaming and Server-Sent Events" subsection under Operation documenting the new sseMetadata property (SdkSseMetadata / SdkSseEventMetadata) that now appears alongside streamMetadata on SdkBodyParameter, SdkMethodResponse, and the HTTP response, including all SdkSseEventMetadata fields (eventType, isTerminalEvent, isEventEnvelope, type/contentType, payloadType/payloadContentType).
• SdkClientType.versionsEnum — documented the new property in the Client section (points to the service's versions enum; undefined for unversioned services and multi-service root clients).
• Boolean @encode(string) — noted that boolean, in addition to integer types, now supports string encoding (encode: "string") in the Built-in Types encode description.

Knowledge base (eng/scripts/doc-updater/knowledge/tcgc.md):

• Recorded lessons for the SSE metadata surface, versionsEnum, boolean string encoding, and the linter-rule fileRef docs (the three active rules are already reflected in reference/linter.md; the removed no-unnamed-types rule is net-unregistered).

**Meta(redacted) updated tcgc.meta.json to the processed checkout commit.

Notes

• All changes verified against the corresponding unit tests (test/methods/sse.test.ts, test/types/built-in.test.ts, test/package/versioning.test.ts).
• The new type-graph surface is emitter-consumed metadata covered by unit tests; no Spector specs or <ClientTabs> examples are required.
• Per-rule reference pages and js-api reference pages are auto-generated via regen-docs (requires a full package + core-submodule build) and are not hand-edited here.

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