Adjust build completion output to report error/warning counts

[seveibar]

Motivation

• Make the final build summary a stronger, machine-parseable signal by reporting total diagnostic counts so artifact generation doesn't mask design errors.
• Ensure worker and sequential build flows both contribute to a single aggregated error/warning tally.

Description

• Add errorCount and warningCount to the BuildFileOutcome, worker BuildCompletedMessage, and BuildJobResult types so counts travel with build results (cli/build/build-file.ts, cli/build/worker-types.ts).
• Compute and propagate per-file diagnostic totals from analyzeCircuitJson in both the sequential and worker paths (cli/build/build-file.ts, cli/build/worker-build-handlers.ts).
• Accumulate totals in the main build command and replace the previous success/failed line with: Build Completed with ${totalErrorCount} errors and ${totalWarningCount} warnings (cli/build/register.ts).
• Wire count propagation through the worker pool result mapping and update a unit test to assert the new completion format (cli/build/worker-pool.ts, tests/cli/build/build-with-drc-error.test.ts).

Testing

• Ran bun test tests/cli/build/build-with-drc-error.test.ts and it passed.
• Ran bunx tsc --noEmit to typecheck and it completed successfully.
• Ran bun run format to format changes and it completed successfully.

---

Codex Task