OSS launch polish: fix hook paths, add OSS files, update README

- Fix slashes in agent identity causing invalid hook file paths (gt-vqhc)
- Add Prerequisites section to README (gt-vzic)
- Create CONTRIBUTING.md, CODE_OF_CONDUCT.md, SECURITY.md (gt-xbfw)
- Update Install section for future package managers (gt-7wcf)

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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

CONTRIBUTING.md

@@ -0,0 +1,61 @@
+# Contributing to Gas Town
+
+Thanks for your interest in contributing! Gas Town is experimental software, and we welcome contributions that help explore these ideas.
+
+## Getting Started
+
+1. Fork the repository
+2. Clone your fork
+3. Install prerequisites (see README.md)
+4. Build and test: `go build -o gt ./cmd/gt && go test ./...`
+
+## Development Workflow
+
+We use a direct-to-main workflow for trusted contributors. For external contributors:
+
+1. Create a feature branch from `main`
+2. Make your changes
+3. Ensure tests pass: `go test ./...`
+4. Submit a pull request
+
+## Code Style
+
+- Follow standard Go conventions (`gofmt`, `go vet`)
+- Keep functions focused and small
+- Add comments for non-obvious logic
+- Include tests for new functionality
+
+## What to Contribute
+
+Good first contributions:
+- Bug fixes with clear reproduction steps
+- Documentation improvements
+- Test coverage for untested code paths
+- Small, focused features
+
+For larger changes, please open an issue first to discuss the approach.
+
+## Commit Messages
+
+- Use present tense ("Add feature" not "Added feature")
+- Keep the first line under 72 characters
+- Reference issues when applicable: `Fix timeout bug (gt-xxx)`
+
+## Testing
+
+Run the full test suite before submitting:
+
+```bash
+go test ./...
+```
+
+For specific packages:
+
+```bash
+go test ./internal/wisp/...
+go test ./cmd/gt/...
+```
+
+## Questions?
+
+Open an issue for questions about contributing. We're happy to help!