🔧 Clean dist before each build

tsc does not prune orphaned emit output, so dropping declarationMap left
stale *.d.ts.map files in dist/ until a manual clean. A prebuild hook now
empties dist/ first, keeping the build reproducible. It deliberately leaves
coverage/ alone, since the manual `clean` resets both.

cspell.json

@@ -28,6 +28,7 @@
         "runwisp",
         "glab",
         "postversion",
+        "prebuild",
         "Zilla",
         "kacl",
         "bestikk",