chore: add REPO_POLICIES compliance files

Add .gitignore, .editorconfig, REPO_POLICIES.md, and .dockerignore
to bring the repository into compliance with REPO_POLICIES standards.

- .gitignore: Standard template from sneak/prompts plus Go-specific entries
- .editorconfig: root=true, UTF-8, LF, tabs for Go/Makefile, 2 spaces elsewhere
- REPO_POLICIES.md: Copied from sneak/prompts (last_modified: 2026-02-22)
- .dockerignore: Excludes .git, bin/, editor configs, docs; keeps all build files

.gitignore

@@ -0,0 +1,31 @@
+# OS
+.DS_Store
+Thumbs.db
+
+# Editors
+*.swp
+*.swo
+*~
+*.bak
+.idea/
+.vscode/
+*.sublime-*
+
+# Node
+node_modules/
+
+# Environment / secrets
+.env
+.env.*
+*.pem
+*.key
+
+# Go
+bin/
+*.exe
+*.exe~
+*.dll
+*.so
+*.dylib
+*.test
+*.out