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.

README.md

@@ -80,7 +80,14 @@ Section "5.1. Installing and playing" has the details.
 - `res/assets/` - where you place your own purchased copy of the game (see
   "3. Game assets" below); `res/assets/extract_assets.sh` extracts it into
   `ss_ee/`.
-- `res/run.sh` - the launcher script, copied into `dist/` on build.
+- `res/run.sh` / `res/run.bat` - the launcher scripts, copied into
+  `dist`/`dist-win` on build. `res/run-mods.sh` / `res/run-mods.bat` are
+  companion launchers that additionally load every mod built under the
+  `modding/` subproject's own `dist/mods/` (see
+  [modding/README.md](modding/README.md) section 4.3) - copied into
+  `dist`/`dist-win` the same way, but not into the redistributable
+  `package`/`package-win` archives, since that build output is local and
+  git-ignored.
 - `res/questshock.config.default.json` - the bundled default configuration
   (see [CONFIG.md](CONFIG.md)); `res/controller_profiles/` - the per-controller
   illustrations and labels shown in the Controller Options tab (see