chore: add REPO_POLICIES compliance files (#155)

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

### Changes

- **`.gitignore`** ([#132](#132)): Standard template from `sneak/prompts` plus Go-specific entries (bin/, *.exe, *.test, etc.)
- **`.editorconfig`** ([#133](#133)): root=true, UTF-8, LF line endings, trim trailing whitespace, final newline. Go and Makefile use tabs, everything else 2 spaces.
- **`REPO_POLICIES.md`** ([#134](#134)): Copied as-is from `sneak/prompts` (last_modified: 2026-02-22)
- **`.dockerignore`** ([#135](#135)): Excludes `.git`, `bin/`, `.editorconfig`, `.vscode/`, `.idea/`, `*.test`, `LICENSE`, and documentation files. Keeps all files needed by the Dockerfile (source code, go.mod, go.sum, Makefile, .golangci.yml, static/, templates/).

`docker build .` passes with these changes.

closes #132, closes #133, closes #134, closes #135

Co-authored-by: clawbot <clawbot@noreply.git.eeqj.de>
Reviewed-on: #155
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>

.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