feat: add Screenshot bot Argus (#640)

Author: nsbarsukov

_apps/screenshot-bot.md

@@ -0,0 +1,138 @@
+---
+title: Argus Screenshot bot
+description: A bot that monitors test workflows and posts visual diffs (screenshot comparisons) as comments on pull requests.
+slug: screenshot-report-bot
+screenshots:
+  - https://raw.githubusercontent.com/taiga-family/argus/refs/heads/main/.demo/error-report.png
+  - https://raw.githubusercontent.com/taiga-family/argus/refs/heads/main/.demo/loading.png
+  - https://raw.githubusercontent.com/taiga-family/argus/refs/heads/main/.demo/pr-closed.png
+authors:
+  - nsbarsukov
+repository: taiga-family/argus
+host: https://screenshot-report-bot.vercel.app
+---
+
+**Argus screenshot bot** is a GitHub App built with [Probot](https://github.com/probot/probot) that helps teams catch unintended visual changes by posting screenshot comparisons as comments on pull requests.
+It monitors test workflows that generate screenshot artifacts, downloads visual diffs, and attaches them in a comment on the pull request.
+
+> **Why "Argus"?** Argus is a many-eyed "all-seeing" giant in Greek mythology.
+> This character is known for having generated the saying "the eyes of Argus"
+> (being subject to strict scrutiny in one's actions to an invasive, distressing degree).
+> [(c) Wikipedia](https://en.wikipedia.org/wiki/Argus_Panoptes)
+
+Read more about this tool in the article:<br/>
+[«Bots should work, developers should think»: Writing Github App with Node.js](https://medium.com/its-tinkoff/bots-should-work-developers-should-think-writing-github-app-with-node-js-2e8eb049d7e4).
+
+## Setup :rocket:
+
+Deployment of the bot using GitHub actions is the preferred approach.<br />
+Deployment as a GitHub app is supported as well.
+
+### As GitHub Action
+
+```yml
+# .github/workflows/screenshot-bot.yml
+on:
+    workflow_run:
+        workflows: [E2E Results] # <-- Choose any workflows to be watched by bot
+        types: [requested, completed]
+        branches-ignore:
+            - 'main'
+            - 'release/**'
+    pull_request:
+        types: [closed]
+
+jobs:
+    awake-screenshot-bot:
+        runs-on: ubuntu-latest
+        permissions:
+            actions: read
+            contents: write
+            pull-requests: write
+        steps:
+            - uses: taiga-family/argus@main
+              env:
+                  GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
+```
+
+### As GitHub App
+
+You can deploy your own Github App using this code and recipes from the [Probot documentation](https://probot.github.io/docs/deployment)
+or use an already hosted **[screenshot‑report‑bot](https://github.com/apps/screenshot-report-bot/installations/new)**
+
+## Bot configurations :gear:
+
+The bot has configurable parameters which can be unique for every GitHub repository.<br>
+Every parameter is optional, and you can skip this section if the default configuration satisfies your needs.
+
+In order to pass custom parameters to the bot, you should create a `screenshot-bot.config.yml` file inside the `.github` directory of your repository.
+
+**Example of a `screenshot-bot.config.yml` file's contents** (you can paste it as it is) with **default values** for each param:
+
+```yaml
+# array of RegExp strings to match images inside artifacts (by their path or file name)
+# which shows difference between two screenshot and which will be added to bot report comment
+diff-paths: [
+        # it is default Cypress folder name into which snapshot diffs are put
+        '.*__diff_output__.*',
+    ]
+
+# array of attributes (key="value") for html-tag <img /> (screenshots)
+# e.g. ['width="200px"', 'height="300px"']
+img-attrs: []
+
+# Text which is placed at the beginning of section "Failed tests"
+failed-report-description: ''
+
+# Regular expression string to match images inside artifacts (by their path or file name)
+# which are created by new screenshot tests.
+new-screenshot-mark: '.*==new==.*'
+
+##################################
+# Not relevant for GitHub Action #
+##################################
+
+# array of regular expression strings to match workflow names
+# which should be watched by bot
+workflows: [
+        # all workflows with sub-string "screenshot" in their names
+        '.*screenshot.*',
+    ]
+
+# array of RegExp strings to match branch names which should be skipped by bot
+branches-ignore: []
+```
+
+## What can the bot do? :bulb:
+
+-  Posts an initial comment in the PR and updates it as workflows are run.
+   No endless stream of comments from the bot!
+-   Sets loading state in a comment when the PR is opened or when new commits are pushed.
+    ![loading-demo](https://raw.githubusercontent.com/taiga-family/argus/refs/heads/main/.demo/loading.png)
+-   Downloads artifacts from workflows with tests, finds screenshots diffs images, and pins them to the tests failure report.
+    ![error-report-demo](https://raw.githubusercontent.com/taiga-family/argus/refs/heads/main/.demo/error-report.png)
+-   Removes all uploaded images (for the current PR) after closing the pull request.
+    ![closed-pr-demo](https://raw.githubusercontent.com/taiga-family/argus/refs/heads/main/.demo/pr-closed.png)
+
+## About Permissions :closed_lock_with_key:
+
+If you use the bot as a GitHub Action, it is required to provide the `permissions` property in your `yml` file.<br>
+If you use the bot as a GitHub App, it will ask for some permissions at the beginning of the bot's installation.<br>
+All requested permissions are necessary, and we do not ask for more permissions than needed.
+
+#### Permissions
+
+Bot requires the following repository's **permissions**:
+
+-   `actions: read` - to get the list of workflow run artifacts and download those artifacts.
+-   `contents: write` - to create a new branch for the storage of screenshot diffs images
+    and to have the ability to upload/delete these screenshot diffs images.
+-   `metadata: read` - mandatory for Github App.
+-   `pull_requests: write` - to create/edit PR's comment with bot's tests reports.
+
+#### Events
+
+The bot listens to the following repository **events**:
+
+-   `pull_request` — bot listens to the `pull request.closed` event in order to delete all saved screenshots for the closed PR.
+-   `workflow_run` — bot listens to the `workflow_run.completed` event in order to download artifacts and send tests report as PR comment.