local-dev: thread pkg/calc into the dockerfile build context

Commit 408097e ('feat: move func to calc package') moved a helper
into pkg/calc and made pkg/util/map.go import galaxy/calc, but the
local-dev backend / gateway Dockerfiles never picked up the new
module. The synthesised go.work has no replace directive for
galaxy/calc and the build context never copies pkg/calc, so any
backend / gateway image rebuild fails with

    galaxy/calc@v0.0.0: malformed module path "galaxy/calc": missing
    dot in first path element

Add the missing COPY, the matching `use ./pkg/calc` line, and the
`galaxy/calc v0.0.0 => ./pkg/calc` replace to both local-dev
Dockerfiles. The local-dev stack now rebuilds cleanly and the
auto-heal flow (prune-broken-engines + pre-bootstrap reconciler
tick) finishes by spawning a fresh engine container for the new
sandbox game.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

tools/local-dev/backend.Dockerfile

@@ -13,6 +13,7 @@ FROM golang:1.26.2-alpine AS builder
 WORKDIR /src
 ENV CGO_ENABLED=0 GOFLAGS=-trimpath
 
+COPY pkg/calc/       ./pkg/calc/
 COPY pkg/cronutil/   ./pkg/cronutil/
 COPY pkg/error/      ./pkg/error/
 COPY pkg/geoip/      ./pkg/geoip/
@@ -28,6 +29,7 @@ go 1.26.2
 
 use (
 	./backend
+	./pkg/calc
 	./pkg/cronutil
 	./pkg/error
 	./pkg/geoip
@@ -39,6 +41,7 @@ use (
 )
 
 replace (
+	galaxy/calc v0.0.0       => ./pkg/calc
 	galaxy/cronutil v0.0.0   => ./pkg/cronutil
 	galaxy/error v0.0.0      => ./pkg/error
 	galaxy/geoip v0.0.0      => ./pkg/geoip

tools/local-dev/gateway.Dockerfile

@@ -11,6 +11,7 @@ FROM golang:1.26.2-alpine AS builder
 WORKDIR /src
 ENV CGO_ENABLED=0 GOFLAGS=-trimpath
 
+COPY pkg/calc/       ./pkg/calc/
 COPY pkg/cronutil/   ./pkg/cronutil/
 COPY pkg/error/      ./pkg/error/
 COPY pkg/geoip/      ./pkg/geoip/
@@ -30,6 +31,7 @@ go 1.26.2
 use (
 	./backend
 	./gateway
+	./pkg/calc
 	./pkg/cronutil
 	./pkg/error
 	./pkg/geoip
@@ -43,6 +45,7 @@ use (
 )
 
 replace (
+	galaxy/calc v0.0.0       => ./pkg/calc
 	galaxy/cronutil v0.0.0   => ./pkg/cronutil
 	galaxy/error v0.0.0      => ./pkg/error
 	galaxy/geoip v0.0.0      => ./pkg/geoip