Reproduce default build discovering work circuits

[ShiboSoftwareDev]

Problem

Running tsci build without a file argument scans every default board pattern before considering the detected main entrypoint. A project with index.circuit.tsx therefore also builds temporary diagnostic circuits under work/, expanding build time and producing unintended outputs.

Reproduction

The focused unit reproduction creates a project containing:

• index.circuit.tsx, the conventional main entrypoint
• work/diagnostic.circuit.tsx, an iterative diagnostic circuit

With no includeBoardFiles configuration and no explicit file/directory argument, getBuildEntrypoints currently returns both files and does not identify the main entrypoint.

The reproduction changes no CLI implementation.

Expected behavior

A no-argument build should use the conventional/configured main entrypoint when one exists. Multi-board discovery remains available through includeBoardFiles or an explicit directory argument.

Verification

• bun test tests/cli/build/build-default-entrypoint-discovery.test.ts
• bun run format:check

The fix will be proposed as a separate PR stacked on this branch.

[github-actions]

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