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.bat

@@ -0,0 +1,20 @@
+@echo off
+setlocal enabledelayedexpansion
+REM Launches System Shock with every mod built under modding\dist\mods\
+REM applied (see modding/README.md section 4). Each mod's own
+REM modding\dist\mods\<name>\mod\ folder is passed to systemshock.exe as a
+REM separate, absolute argument - see run-mods.sh's comment for why (same
+REM engine, same one-level directory scan and same relative-path pitfall).
+cd /d "%~dp0"
+
+set "MODS_DIR=%~dp0..\modding\dist\mods"
+set "MOD_ARGS="
+
+if exist "%MODS_DIR%" (
+    for /d %%M in ("%MODS_DIR%\*") do (
+        if exist "%%M\mod" set "MOD_ARGS=!MOD_ARGS! "%%~fM\mod""
+    )
+)
+
+systemshock.exe !MOD_ARGS! %*
+exit /b %errorlevel%