Integrate fizzy-saas as vendored gem at saas/

- Update Gemfile.saas to use path: "saas" instead of GitHub source
- Update config/database.yml to reference local saas/ directory
- Update bin/setup to source saas/bin/setup directly
- Remove redundant dotfiles (ruby-version, gitignore, rubocop, github workflows)
- Add saas/db exclusions to root rubocop config

.rubocop.yml

@@ -11,3 +11,5 @@ AllCops:
   Exclude:
     - 'db/migrate/**/*'
     - 'db/schema*.rb'
+    - 'saas/db/migrate/**/*'
+    - 'saas/db/saas_schema.rb'