professionalize repo for public release

- rename ctcloud -> bucketeer everywhere (cmd/bucketeer, binary, compose service)
- group brand assets under assets/ (light/dark logo + UI screenshot)
- move long-form docs under docs/ (ARCHITECTURE, DESIGN, GOAL) and add
  docs/SKILL.md: how an agent queries/audits a running instance and answers
  user questions from the API and PostgreSQL
- README: large logo (light/dark picture) and UI screenshot, repository layout
- .gitignore: /bucketeer, .env, pgdata, build/test artifacts, OS junk
- .dockerignore: keep brand/docs/markdown out of the build context

.dockerignore

@@ -1,6 +1,10 @@
 .git
 .gitignore
+.env
 pgdata
 *.test
 *.out
 .gocache
+assets
+docs
+*.md