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-run-image.sh

@@ -0,0 +1,51 @@
+#!/usr/bin/env bash
+# Runs the mdlp-image to build the mod(s) defined under modding/mods/ (see
+# README.md) into modding/dist/mods/, entirely offline - every Go module
+# dependency mdlp needs was already fetched into the image by
+# ./mdlp-image.sh.
+#
+# Mounts the whole repository, not just modding/, because mdlp also needs the
+# game's own data directory (res/assets/ss_ee/data) as read-only reference
+# data (see the root README.md section 3 for how that gets populated).
+#
+# Usage: MODS="name1 name2" ./mdlp-run-image.sh [command...]
+#   With no arguments, runs the image's baked-in process-mods.sh (its default
+#   CMD), building every mod under mods/ (or only those named in MODS, if
+#   set). Pass a command (e.g. `bash`) to get a shell in the build
+#   environment instead, useful for debugging a failed build.
+set -euo pipefail
+
+cd "$(dirname "${BASH_SOURCE[0]}")"
+MODDING_ROOT="$(pwd)"
+REPO_ROOT="$(cd .. && pwd)"
+
+fail() { echo "PREFLIGHT FAIL: $*" >&2; exit 1; }
+
+command -v docker >/dev/null 2>&1 \
+    || fail "docker not found in PATH"
+
+IMAGE="${MDLP_REGISTRY_IMAGE:-questshock/mdlp}"
+if [ -f "$MODDING_ROOT/../registry.env" ]; then
+    # shellcheck disable=SC1091
+    source "$MODDING_ROOT/../registry.env"
+    IMAGE="${MDLP_REGISTRY_IMAGE:-$IMAGE}"
+fi
+
+IMAGE_TAG="$(<"$MODDING_ROOT/mdlp-image/VERSION")"
+[ -n "$IMAGE_TAG" ] || fail "mdlp-image/VERSION is empty"
+IMAGE="$IMAGE:$IMAGE_TAG"
+
+docker image inspect "$IMAGE" >/dev/null 2>&1 \
+    || fail "$IMAGE not found locally - run ./mdlp-image.sh first"
+
+TTY_FLAGS="-i"
+[ -t 1 ] && TTY_FLAGS="-it"
+
+# shellcheck disable=SC2086
+docker run --rm $TTY_FLAGS \
+    -v "$REPO_ROOT:/workspace" \
+    -e HOST_UID="$(id -u)" \
+    -e HOST_GID="$(id -g)" \
+    -e MODS="${MODS:-}" \
+    "$IMAGE" \
+    "$@"