[codex] Add column store quickstart

[snissn]

Summary

Adds a standalone TreeDB column-store quickstart under examples/column_store_quickstart.

The walkthrough writes a small activity-event stream, stores time_us, action, and actor in physical column lanes, reopens the database, reads one row back by id, and runs two explicit physical column scans:

• events_by_action
• active_window_by_actor

The terminal output is framed with narrative text, boxed sections, and readable scan counters so the example feels like a motivated use case rather than a raw harness.

Validation

• GOWORK=off go run . from examples/column_store_quickstart
• GOWORK=off go test ./examples/column_store_quickstart
• git diff --cached --check before commit

[coderabbitai]

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✨ Finishing Touches

🧪 Generate unit tests (beta)

✅ Unit Test PR creation complete.

• Create PR with unit tests
• Commit unit tests in branch codex/column-store-quickstart

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[coderabbitai]

Note

Unit test generation is a public access feature. Expect some limitations and changes as we gather feedback and continue to improve it.

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Generating unit tests... This may take up to 20 minutes.

[coderabbitai]

✅ Created PR with unit tests: #1639

[snissn]

Closing this as stale/deferred rather than retargeting it through the current production stack.

Read-only validation against current origin/main shows the branch is still based on the older M15C column-store stack and would be destructive if retargeted: it removes current production column-store/query/vector graph files, docs, demos, scripts, and tests while adding the standalone examples/column_store_quickstart material. The quickstart itself may still be useful, but it should be re-extracted as a fresh small docs/example PR on current main if we want it.

This keeps the merge-prep batch focused on current production code and avoids carrying a stale draft branch through the stack.