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

.env.example

@@ -1,14 +1,14 @@
 # Copy to .env and edit. .env is gitignored.
 
-POSTGRES_USER=ctcloud
+POSTGRES_USER=bucketeer
 POSTGRES_PASSWORD=change-me-strong
-POSTGRES_DB=ctcloud
+POSTGRES_DB=bucketeer
 
 # Local compose (private bridge network, no TLS):
-DATABASE_URL=postgres://ctcloud:change-me-strong@postgres:5432/ctcloud?sslmode=disable
+DATABASE_URL=postgres://bucketeer:change-me-strong@postgres:5432/bucketeer?sslmode=disable
 
 # Production: use a TLS-enabled database instead, e.g.
-# DATABASE_URL=postgres://user:[email protected]:5432/ctcloud?sslmode=verify-full
+# DATABASE_URL=postgres://user:[email protected]:5432/bucketeer?sslmode=verify-full
 
 # DNS_SERVERS unset = ~20 curated public resolvers. Options:
 #   DNS_SERVERS=system             use the OS resolver