[codex] fix fallow dead code

[KeKs0r]

Summary

Fixes the Fallow dead-code report by removing unused exports, stale barrel re-exports, unused local declarations, and unused package dependencies.

What changed

• Removed unused value and type exports across CLI, core, backfill, codegen, and ObsessionDB plugin packages.
• Removed unused local declarations that became visible after export cleanup.
• Removed unused dependencies from package manifests and reconciled bun.lock.
• Kept the unrelated local .gitignore change out of this commit.

Impact

This reduces the public/internal TypeScript surface area to only the symbols with known consumers and clears the dead-code gate without changing runtime behavior for used APIs.

Validation

• bunx fallow dead-code passes with no issues.
• bun run typecheck passes.
• bun run lint exits successfully, with existing unrelated style warnings still reported.
• bun run build passes.
• bun run fallow:pr reports dead code clean, with existing duplication/health advisories still present.
• bun run test is blocked by missing ClickHouse e2e env (CLICKHOUSE_URL or CLICKHOUSE_HOST) in packages/core/src/sql-validation.e2e.test.ts.