Fix hacked GTK3/GLFW crash by vendoring a patched sqweek/dialog

The built hacked binary segfaults on Linux the moment a native GTK3
dialog (file/folder browse) opens while a GLFW/OpenGL context is live:
sqweek/dialog's Linux backend never calls XInitThreads() before
gtk_init(), and GLFW's own X11 backend installs a process-wide Xlib
error handler that collides with GTK's.

Vendor a pinned copy of github.com/sqweek/dialog (New BSD) into
modding/sqweek-dialog/ so it can be patched like every other vendored
source here: sqweek-dialog-patches/01-xinitthreads.patch adds the
missing XInitThreads() call, and hacked-patches/01-use-patched-dialog.patch
adds a go.mod replace directive pointing hacked's own sqweek/dialog
dependency at that local copy. build-hacked.sh now stages both hacked/
and sqweek-dialog/ into a scratch modding/build/ directory and applies
their patch series before compiling, rather than building hacked/ in
place; .gitignore picks up that new scratch directory.

Also expand modding/README.md: number its existing sections and add a
worked "Example: Editing a message" walkthrough covering Static World
Data, the Messages window's clipboard-only text editing, saving the
Mod Location, and the absolute-path requirement for run.sh's mod-folder
argument.

modding/sqweek-dialog/.golangci.yml

@@ -0,0 +1,16 @@
+run:
+  deadline: 5m
+
+linters:
+  enable-all: true
+
+  # linters are disabled if their majority of issues is considered false-positive (intended code)
+  # and the remaining issues (if existing) aren't worth it.
+  disable:
+    - gochecknoinits
+    - gochecknoglobals
+
+issues:
+  exclude-use-default: false # disable filtering of defaults for better zero-issue policy
+  max-per-linter: 0 # disable limit; report all issues of a linter
+  max-same-issues: 0 # disable limit; report all issues of the same issue