Stream large database exports

[Gimyoonsoo]

Summary

• Improves the large export behavior described in Database dumps do not work on large databases #59.
• Streams SQL dump, CSV, and JSON export responses instead of building full export payloads in memory first.

Changes

• Add shared streaming export helpers and batched table reads.
• Update database dump export to stream table schemas and row inserts.
• Update CSV and JSON table exports to stream batches while preserving file download headers.
• Add focused tests for streamed dump, CSV, JSON, batched reads, and stream responses.

Testing

• .\node_modules.bin\vitest.exe run src/export
• Result: passed, 31 passed / 0 failed
• .\node_modules.bin\prettier.exe --check src/export/index.ts src/export/dump.ts src/export/csv.ts src/export/json.ts src/export/index.test.ts src/export/dump.test.ts src/export/csv.test.ts src/export/json.test.ts
• Result: passed
• git diff --check
• Result: passed, with line-ending warnings only
• .\node_modules.bin\vite.exe build --mode client; if ($LASTEXITCODE -eq 0) { .\node_modules.bin\vite.exe build }
• Result: passed; build printed existing non-fatal Failed to find Response internal state key warnings
• .\node_modules.bin\tsc.exe --noEmit --pretty false
• Result: failed because of existing unrelated errors in plugins/cdc, src/cache, src/do, and src/operation; no errors pointed to the modified export files.

Notes

• No authentication, payment, database, deployment, or security-sensitive configuration changes were made.
• No secrets, credentials, production data, or security-sensitive information were accessed.

Algora

/claim #59