Add production S3-to-ClickHouse modeling examples

[rohithreddykota]

Summary

• convert all nine ClickHouse modeling examples from ClickHouse-to-DuckDB exports into S3-to-ClickHouse ingestion
• add production and development partition definitions, idempotent partition overwrite, versioned merge patterns, TTLs, sorting and primary keys, explicit schemas, and skipping indexes
• document overwrite-boundary safety, state watermark overlap, S3 deletion limitations, and gallery startup behavior
• add a static validation script for the ClickHouse examples

Test plan

• rill-modeling-examples/scripts/check_examples.sh
• bash -n rill-modeling-examples/scripts/check_examples.sh
• git diff --check origin/main...HEAD

The Rill project was not started or queried; verification was static only.

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