Add a first-party MDL mod-build system and reorganize modding/ under src/

modding/mods/ holds message edits as plain JSON (type, index, language,
plus only the changed fields - a long body can live in a sibling .txt to
avoid escaping in JSON), so mod authoring is reviewable in git instead of
living only in hacked's GUI. mdlp (modding/src/mdlp/, its own Docker image
mdlp-image/) turns them into the same mod folder/zip hacked's own Save
produces, reusing hacked's ss1/edit, ss1/world and ss1/content/text
packages via a go.mod replace - no GUI/GLFW/GTK needed. `make mods`
builds every mod into dist/mods/<name>/, scoped per-mod so it never
touches hacked's own build output; `make` (no target) now builds both.

Fixes a bug this surfaced: hacked's FileLocation.AbsolutePathFrom
silently writes into the current directory instead of the given output
folder when passed a relative path (the GUI never hits this since its
folder picker is always absolute) - mdlp now resolves its own paths
up front.

res/run-mods.sh/.bat are new companion launchers to run.sh/.bat: they
pass every dist/mods/*/mod folder to the engine as a separate absolute
argument, since ProcessModDirectory() only scans one directory level
deep. Wired into `make dist`/`dist-win` only, not the release archives.

modding/hacked/, its patches, sqweek-dialog/, its patches, and the new
mdlp/ move under modding/src/, separating source from the surrounding
Docker/script scaffolding; all path references updated to match.

NOTICE.txt gains a section for hacked's distributed build, listing hacked
(New BSD), sqweek/dialog (ISC - corrected from a wrong "New BSD" note),
and hacked's other direct Go dependencies.

modding/mdlp-upload-image.sh

@@ -0,0 +1,40 @@
+#!/usr/bin/env bash
+# Pushes the mdlp-image - already built locally with ./mdlp-image.sh, and
+# ideally verified with ./mdlp-run-image.sh - to a container registry, so CI
+# or other machines can reuse it without rebuilding the whole toolchain.
+set -euo pipefail
+
+cd "$(dirname "${BASH_SOURCE[0]}")"
+ROOT="$(pwd)"
+
+fail() { echo "PREFLIGHT FAIL: $*" >&2; exit 1; }
+
+command -v docker >/dev/null 2>&1 \
+    || fail "docker not found in PATH"
+
+[ -f "$ROOT/../registry.env" ] \
+    || fail "../registry.env not found - copy ../registry.env.example to ../registry.env and fill in your registry credentials"
+
+# shellcheck disable=SC1091
+source "$ROOT/../registry.env"
+
+: "${REGISTRY:?registry.env must set REGISTRY}"
+: "${REGISTRY_USER:?registry.env must set REGISTRY_USER}"
+: "${REGISTRY_PASSWORD:?registry.env must set REGISTRY_PASSWORD}"
+MDLP_REGISTRY_IMAGE="${MDLP_REGISTRY_IMAGE:-questshock/mdlp}"
+
+VERSION="$(<"$ROOT/mdlp-image/VERSION")"
+[ -n "$VERSION" ] || fail "mdlp-image/VERSION is empty"
+
+docker image inspect "$MDLP_REGISTRY_IMAGE:$VERSION" >/dev/null 2>&1 \
+    || fail "$MDLP_REGISTRY_IMAGE:$VERSION not found locally - run ./mdlp-image.sh first"
+
+echo "== Logging in to $REGISTRY =="
+echo "$REGISTRY_PASSWORD" | docker login "$REGISTRY" -u "$REGISTRY_USER" --password-stdin
+
+echo "== Pushing $MDLP_REGISTRY_IMAGE:$VERSION and :latest =="
+docker push "$MDLP_REGISTRY_IMAGE:$VERSION"
+docker push "$MDLP_REGISTRY_IMAGE:latest"
+
+echo "== Done =="
+echo "Image: $MDLP_REGISTRY_IMAGE:$VERSION"