[Automated][tcgc] Update emitter guideline for versionsEnum, SSE metadata, and boolean encode

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Summary

Incremental documentation update for TCGC based on 8 source commits since the last checkpoint. Most commits were pure formatting/eslint-comment changes; this PR covers the three substantive, user-observable additions plus the removal of a linter rule, and records lessons in the knowledge base.

Changes

Emitter developer docs (guideline.md):

• SdkClientType.versionsEnum — documented the new field exposing the service's API-versions SdkEnumType on each client (undefined for unversioned/multi-service clients).
• SSE metadata — documented the new SdkSseMetadata / SdkSseEventMetadata carried on HTTP body parameters and responses for text/event-stream (@events) streams, alongside streamMetadata.
• Boolean @encode(string) — updated the built-in types note; @encode(string) now applies to boolean in addition to integer kinds, setting encode: "string".

Knowledge base (knowledge/tcgc.md):

• Recorded lessons for the above, plus a note that the no-unnamed-types linter rule was removed (and unregistered) and that the remaining rule .md bodies were expanded (Impact / Diagnostic Message / How to Fix / Suppression). Regenerating reference/rules/*.md requires a full pnpm regen-docs build and was out of scope for this constrained run.

Metadata (knowledge/tcgc.meta.json):

• Updated checkout commit via update-meta.ts so the next incremental run starts from the correct point.

Notes

No Spector specs were added — these are emitter-consumed type-graph metadata and type encode behavior covered by existing unit tests, not new wire-level scenarios. No <ClientTabs> blocks were added or changed.

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