Add versioning and dist packaging target

VERSION in makefile is now the single source of truth — it flows into
the about screen via -DAPP_VERSION at compile time and into the archive
filename via the dist target. `make dist` produces
SoundThing-<platform>-v<version>.tar.gz (Linux) or .zip (Windows)
containing the binary and the full patch library.

Also fixes a trailing-spaces-in-PROJECT makefile gotcha that was
silently embedding spaces in the binary path.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

source/ui.c

@@ -1691,7 +1691,7 @@ void uiAboutMenu(UIState *ui, float x, float y, float width)
 
     /* Edit these strings to update the about screen. */
     static const char *lines[] = {
-        "SoundThing  v0.9.5",
+        "SoundThing  v" APP_VERSION,
         "",
         "Polyphonic subtractive synthesizer",
         "Built with Raylib",