[P2][router] add route collision and shadowing diagnostics

[redpeacock78]

Summary

Route registration currently appends routes in order and dispatches by first match. That is simple and useful, but H-awk should warn about duplicate routes and likely shadowing once the framework grows route files/grouping/plugins.

Evidence

• core/router.awk stores each route in ROUTES[method, path, ...] and appends registration order to ROUTES_ORDER.
• Dispatch scans ROUTES_ORDER sequentially and runs the first matching route with the same method.
• Dynamic segments such as /:id can shadow more specific routes registered later.

Proposed feature

• Detect exact duplicate method + path registrations.
• Warn when a dynamic route probably shadows a later static route.
• Optionally expose hawk check diagnostics for route tables.
• Add a debug command to print route order and compiled regex patterns.

Acceptance criteria

• Duplicate route registration is detected.
• Common shadowing cases are reported with file/line info if available.
• Users can intentionally suppress/allow a duplicate route when needed.
• Tests cover exact duplicate, static-before-dynamic, and dynamic-before-static order.

Priority: P2
Area: router/diagnostics
Type: feature