Add pre-aggregate best practices and semantic layer note

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Summary

• Added a tip about date granularity behavior: day-level pre-aggregates serve day/week/month/quarter/year queries, while month-level only serves month/quarter/year (not day or week)
• Added best practice guidance to prefer multiple small, focused pre-aggregates over a single large one with all metrics and dimensions
• Documented that any query through the Lightdash semantic layer (app, API, MCP, AI agents, Embed SDK, React SDK) can hit pre-aggregate cache

Files changed

• references/pre-aggregates/overview.mdx — granularity tip + semantic layer note
• references/pre-aggregates/getting-started.mdx — best practice on small pre-aggregates

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Project	Status	Preview	Updated (UTC)
lightdash	🟢 Ready	View Preview	Apr 2, 2026, 11:47 AM

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