Keep route-proxy's contract a package of its own module, not a second module behind a replace

The group's check failed at go mod verify: the build module's workspace carries one module, so the replace of
./contract named a go.mod it never placed; and ADR 0573 clause 1 refuses a path into another tree. Nothing outside
route-proxy imports the contract today; when one must, it moves into the networking domain's package (research 081).
Issue 1126.

Claude-Session: https://claude.ai/code/session_01NcbgfJ9Gum47zkFKWRaovL

modules/route-proxy/README.md

@@ -17,11 +17,11 @@ consumer on its own machine.
 
 ## Its contract: a package of its own
 
-**route-proxy defines its own contract, and other modules use it** (the operator, 2026-10-31). It is the Go module
-`git.novox.be/novox/mesh-networking/modules/route-proxy/contract`, in `contract/` here with its own `go.mod`, standard
-library only, released by tags `modules/route-proxy/contract/vX.Y.Z` of this repository, the way mesh-sdk is released
-(`go/vX.Y.Z`); another module depends on it by its version like any other, and this module builds it from its own
-tree (a `replace` of `./contract` in `go.mod`), so the two never drift. It holds:
+**route-proxy defines its own contract** (the operator, 2026-10-31). It is the package `contract` of this module
+(`route-proxy/contract`), standard library only, built from the same tree, so the two never drift. No `replace` to a
+directory and no second module: ADR 0573 clause 1 refuses a path into another tree, and the build module's workspace
+carries one module. No other module imports it today; when one must, the contract moves into the networking domain's
+package, as research 081 (how seats are defined) decides. It holds:
 
 - **the route a consumer asks** (`Request`, read strictly by `DecodeRequest`: no field it does not name, a name of
   either kind, a port where the rule forwards, http or https, a positive body limit, a secret's file never a