docs: add devops.md detailing release workflow

docs/devops.md

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+# DevOps Release Workflow
+
+This document describes the deployment and release process for KoalaSync.
+
+## Tag-Based Releases
+
+KoalaSync uses a fully automated release pipeline triggered by Git tags. 
+
+> [!IMPORTANT]
+> **DO NOT** manually bump the version numbers in any files (such as `package.json`, `manifest.base.json`, `shared/constants.js`, etc.) before creating a release. 
+> Bumping versions manually is redundant, leads to conflicts, and is completely handled by the CI/CD pipeline.
+
+### How it Works
+
+When you push a Git tag matching `v*` (e.g., `v2.5.1`), the GitHub Actions release workflow (`.github/workflows/release.yml`) is triggered. The workflow performs the following actions:
+
+1. **Extracts the version** from the tag (e.g., `2.5.1` from `v2.5.1`).
+2. **Injects the version** automatically into the following files:
+   - `extension/manifest.base.json`
+   - `shared/constants.js` (updates `APP_VERSION`)
+   - `package.json`
+   - `website/version.json`
+   - `website/template.html` (updates `softwareVersion` schema)
+   - `README.md` (updates badge and announcement banner)
+   - `website/sitemap.xml` (updates `lastmod` dates)
+3. **Commits and pushes** these version updates back to the `main` branch automatically with the commit message `chore(release): update versions to vX.X.X [skip ci]`.
+4. **Builds the extension** for both Chrome and Firefox and publishes the zipped archives.
+5. **Builds the website** and uploads website artifacts.
+6. **Builds and publishes** the Docker image for the relay server to the GitHub Container Registry (`ghcr.io`).
+
+---
+
+## Steps to Deploy a New Release
+
+To release a new version (e.g., `v2.5.1`), follow these steps:
+
+1. Make sure your local repository is synced on `main`:
+   ```bash
+   git checkout main
+   git pull origin main
+   ```
+2. Create a local Git tag:
+   ```bash
+   git tag v2.5.1
+   ```
+3. Push the tag to GitHub:
+   ```bash
+   git push origin v2.5.1
+   ```
+
+The release pipeline will take care of the rest! You can monitor the progress under the **Actions** tab of the GitHub repository.