Add design doc for generic OpenHouseTable operation summary accumulator (commits and scans)

[devin-ai-integration]

Summary

Adds a design document for a generic, reusable operation summary accumulator for OpenHouse Iceberg tables. The design introduces a generic OpenHouseTable wrapper that delegates to the real Table and overrides data-file mutation entry points (newAppend, newFastAppend, newOverwrite, newReplacePartitions, newDelete, newTransaction) and scan entry points (newScan, newIncrementalAppendScan, newIncrementalChangelogScan). Business logic is injected through OpenHouseTableListener; the first listener is OpenHouseTableSummaryAccumulator, which produces an OpenHouseTableSummary whose partition-level objects have the same shape as CommitEventTablePartitions and CommitEventTablePartitionStats from TableStatsCollector. Adapters convert summaries to driver logs, lineage events, and a server request attachment.

All core components live in the existing openhouse-java-runtime module; adapters live in apps/spark where services:common is already on the classpath.

Changes

• Documentation

Testing Done

• No tests added or updated. This PR only adds a design document; implementation and tests will follow in a subsequent change.

Additional Information

• Breaking Changes
• Deprecations
• Large PR broken into smaller PRs, and PR plan linked in the description.

Link to Devin session: https://app.devin.ai/sessions/a4ab4df6bc134ac5ab00ec63abcd854c
Open in Devin Desktop: https://app.devin.ai/desktop/session/a4ab4df6bc134ac5ab00ec63abcd854c?variant=devin
Requested by: @cbb330

[devin-ai-integration]

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