✨ feat(sources): add opt-in source content lookup

[marcelsamyn]

What and why

Add an explicit source-content read path to the SDK and API without loading source payloads during node-source lookup.

• Extend MemoryClient.getSource / POST /sources/get with includeContent?: boolean.
• Return stored textual content as { text, format } | null only when requested.
• Never decode or return raw binary blobs.
• Make getNodeSources metadata-only and remove its eager payload reads.
• Update MCP wording and consumer migration documentation.

Developer impact

This is a breaking cleanup for consumers of getNodeSources: the returned source items no longer contain content. Consumers that need source text should call getSource({ userId, sourceId, includeContent: true }) explicitly.

How to test

• pnpm test --run (383 tests)
• pnpm run build:check
• pnpm run build-sdk
• pnpm run lint
• pnpm run format
• pnpm run build

Checklist

• Build
• Tests
• Lint
• Prettier
• SDK export verification
• Breaking change documented

[gemini-code-assist]

Code Review

This pull request refactors source content retrieval by restricting the node-sources endpoint to metadata-only and moving content lookup to the single-source endpoint. Specifically, MemoryClient.getNodeSources (and the get node sources MCP tool) no longer fetches or returns raw source content. Instead, consumers can retrieve a source's stored textual representation by calling MemoryClient.getSource with the new includeContent: true parameter. These changes are accompanied by updated schemas, documentation, and comprehensive test coverage. I have no feedback to provide as there are no review comments.

Important

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