Add CONTRIBUTING.md, CI workflow, issue/PR templates

- CONTRIBUTING.md: setup guide, code style, PR process
- GitHub Actions CI: cargo check, test, clippy, fmt on every push/PR
- Issue templates: feature request + bug report
- PR template with checklist

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: abhicris

.github/ISSUE_TEMPLATE/bug.md

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+---
+name: Bug Report
+about: Report a bug
+title: '[Bug] '
+labels: 'bug'
+---
+## Describe the Bug
+## Steps to Reproduce
+## Expected Behavior
+## Environment
+- OS:
+- Rust version:
+- arka version:

.github/ISSUE_TEMPLATE/feature.md

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+---
+name: Feature Request
+about: Suggest a new feature
+title: '[Feature] '
+labels: 'help-wanted'
+---
+## Summary
+## Motivation
+## Proposed Solution

.github/pull_request_template.md

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+## What
+<!-- What does this PR do? -->
+
+## Why
+<!-- Why is this change needed? -->
+
+## How to Test
+<!-- Steps to verify the change -->
+
+## Checklist
+- [ ] `cargo test` passes
+- [ ] `cargo clippy` passes
+- [ ] Docs updated if API changed

.github/workflows/ci.yml

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+name: CI
+on: [push, pull_request]
+jobs:
+  check:
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v4
+      - uses: dtolnay/rust-toolchain@stable
+      - run: cargo check --all-features
+      - run: cargo test
+      - run: cargo clippy -- -D warnings
+      - run: cargo fmt -- --check

CONTRIBUTING.md

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+# Contributing to arka
+
+Thanks for your interest in contributing! arka is a [kcolbchain](https://kcolbchain.com) open-source project.
+
+## Quick Start
+
+```bash
+git clone https://github.com/YOUR_USERNAME/arka.git
+cd arka
+cargo build
+cargo test
+```
+
+## Finding Work
+
+- [Open issues](https://github.com/kcolbchain/arka/issues)
+- `good-first-issue` — great starting points
+- `help-wanted` — needs community help
+- Comment on an issue before starting work
+
+## Code Style
+
+- `cargo fmt` before committing
+- `cargo clippy` should pass with no warnings
+- Write doc comments for public functions
+- Add tests for new functionality
+
+## PR Process
+
+1. One feature/fix per PR
+2. `cargo test` must pass
+3. `cargo clippy` must pass
+4. Update README if you changed the API
+
+## Community
+
+- [kcolbchain.com](https://kcolbchain.com) | [Join](https://kcolbchain.com/join.html) | [GitHub](https://github.com/kcolbchain)
+
+## License
+
+MIT — contributions licensed under the same.