build: add Maven wrapper and prebuilt release jar; ignore docs/superpowers

- Add ./mvnw wrapper (script-only) so the project builds/runs without a
  system Maven install.
- Add maven-shade-plugin producing a self-contained release/HauntedManor.jar
  (merges audio SPI services; no dependency-reduced-pom).
- Document running via ./mvnw and via the jar directly in the README.
- Ignore docs/superpowers/ (planning specs kept locally, untracked).

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

Semesterprojekt/.gitignore

@@ -41,6 +41,9 @@ build/
 ### Brainstorming visual companion ###
 .superpowers/
 
+# Planning specs & implementation plans (kept locally, not tracked)
+docs/superpowers/
+
 # Local save games and settings
 saves/