Update project config for Go tool and port change

Add Go to .tool-versions, update .gitignore for Go build output and
cache, document seed data regeneration in README, and change API port
from 8000 to 8080 in docker-compose.

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

docker-compose.yml

@@ -4,7 +4,7 @@ services:
       context: ./backend
       dockerfile: Dockerfile
     ports:
-      - "8000:8000"
+      - "8080:8000"
     volumes:
       - ./backend/src:/app/src:cached
       - ./backend/alembic.ini:/app/alembic.ini:cached
@@ -27,7 +27,7 @@ services:
       - ./frontend/public:/app/public:cached
       - ./frontend/index.html:/app/index.html:cached
     environment:
-      - VITE_API_URL=http://localhost:8000
+      - VITE_API_URL=http://localhost:8080
     depends_on:
       - api
     restart: unless-stopped