build(build-tools): migrate fluid-build to use build-infrastructure for repo layout

[tylerbutler]

Description

Migrates fluid-build from its internal FluidRepo/MonoRepo/Package classes (all marked @deprecated) to use @fluid-tools/build-infrastructure's BuildProject/IReleaseGroup/IPackage for repo layout discovery. Also adds a new flub build oclif command in build-cli as a thin wrapper around the build engine.

Architecture:

• FluidRepoBuild now composes a BuildProject (via loadBuildProject) instead of extending FluidRepo
• FluidBuildPackage wraps IPackage with build-specific state (matched, getLockFilePath, etc.)
• Local structural types in buildInfraTypes.ts solve CJS/ESM interop (build-infrastructure is ESM-only, build-tools emits CJS)
• The deprecated FluidRepo, MonoRepo, Package exports are preserved for backward compatibility

New flub build command:

• All fluid-build flags mapped to oclif flags
• Delegates to the same FluidRepoBuild engine
• fluid-build binary continues to work during transition

Reviewer Guidance

The review process is outlined on this wiki page.

• This is an early draft/proof-of-concept. The CJS/ESM interop approach (local structural types + dynamic import) works but is worth discussing — alternatives include adding a CJS build to build-infrastructure or converting build-tools to ESM.
• The global options singleton from options.ts is still used by the build engine. The flub build command populates it via Object.assign before calling the engine. A future PR should thread options through BuildContext instead.
• The flub build command has a minor cosmetic issue where positional package args may appear in the task name log line.
• Tested manually: fluid-build and flub build both produce identical build results. All 137 existing tests pass.

[github-actions]

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