Middleware pipeline #1906

Phase 1 — Modernization Target #1

Add a global and route-scoped middleware pipeline that runs before/after the controller filter chain, replacing ad-hoc plugin mixins for cross-cutting concerns.

Design

• Middleware CFC implements handle(request, next) contract
• wheels.middleware.Pipeline chains middleware with a next closure
• Dispatch.cfc:$request() wraps controller dispatch in the pipeline
• middleware parameter on Mapper route definitions
• Ship built-in: RequestId, Cors, SecurityHeaders

Backwards Compatibility

Existing controller filters() continue to work unchanged. Middleware runs at the dispatch level (before controller instantiation), while filters run inside the controller.

See design_docs/MODERNIZE-WHEELS-RIM.md §4.1 for full implementation plan.