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.

res/run-mods.sh

@@ -0,0 +1,21 @@
+#!/usr/bin/env bash
+# Launches System Shock with every mod built under modding/dist/mods/
+# applied (see modding/README.md section 4). Each mod's own
+# modding/dist/mods/<name>/mod/ folder is passed to run.sh as a separate,
+# absolute argument - the engine's ProcessModDirectory()
+# (engine/src/MacSrc/Modding.c) only scans one directory level deep, so it
+# can never be pointed at modding/dist/mods/ itself and find the mods nested
+# a level further inside, and a relative argument would resolve against the
+# wrong directory once run.sh changes into its own.
+set -euo pipefail
+cd "$(dirname "${BASH_SOURCE[0]}")"
+
+MODS_DIR="$(pwd)/../modding/dist/mods"
+MOD_ARGS=()
+if [ -d "$MODS_DIR" ]; then
+    for mod in "$MODS_DIR"/*/mod; do
+        [ -d "$mod" ] && MOD_ARGS+=("$(cd "$mod" && pwd)")
+    done
+fi
+
+exec ./run.sh "${MOD_ARGS[@]}" "$@"