fix(compiler): reject dynamic default contract routes

[cssbruno]

Summary

• Stop deriving generated contract route paths from dynamic page route patterns when g:command or g:query omits an explicit action/path.
• Emit contract_route_invalid for omitted contract routes on dynamic pages so the route report cannot advertise unreachable /path/{param} backend routes.
• Add a regression for default command routes colliding with inherited page action routes so appgen duplicate backend registrations stay compile-time diagnostics.

Review Feedback

Addresses Codex review comments:

• Avoid registering template route patterns for default commands.
• Detect collisions with page-owned backend endpoints.

Verification

• go test ./internal/gwdkanalysis ./internal/compiler
• go test ./internal/appgen ./internal/buildgen
• go test ./...
• go build ./cmd/gowdk

LLM Assistance

• Implemented by Codex from automated review feedback.