AIT-27: Add CodeRabbit AI code review configuration

[devin-ai-integration]

I have created this PR because

This PR implements CodeRabbit AI code review tool configuration for the purple-stack repository as requested in Linear ticket AIT-27. The goal is to enable automated code review assistance that provides security scanning, best practice enforcement, and consistency checks for pull requests in this full-stack serverless repository.

This follows the reference implementation pattern from PTT-2623 (admin-tool repository), adapted for purple-stack's SST/Next.js/TypeScript serverless architecture.

What changed

Added .coderabbit.yaml configuration file (530 lines) with the following key settings:

Review Configuration:

• Review profile: "chill" (balanced feedback, not overly nitpicky)
• Auto-review enabled with incremental reviews on each push
• Reviews both master and staging branch PRs
• Skips draft PRs and PRs with "wip" in title

Enabled Security/Quality Tools:

• ESLint - JavaScript/TypeScript linting
• Gitleaks - Secret scanning
• OSV Scanner - Dependency vulnerability scanning
• YAMLlint - YAML file validation
• LanguageTool - Grammar/style checking

Disabled Tools:

• Checkov (infrastructure-as-code scanner - not needed for this repo)
• ShellCheck, markdownlint, actionlint, SQLFluff, Oxlint

Linear Integration:

• Team keys: [PTT, MTE, AIT] - added AIT for this ticket
• PR title requirement: Must start with ticket ID (e.g., "AIT-27: ...")
• Knowledge base integration enabled for local learnings

Code Generation:

• Unit test generation: enabled
• Docstring generation: disabled

Important notes for reviewers

⚠️ Prerequisites: This configuration requires the CodeRabbit GitHub App to be installed for the purple-technology organization or this repository. Please verify the app is installed before merging.

🔍 Review focus areas:

1. Verify that base_branches: [staging] matches our deployment workflow (master + staging)
2. Confirm "AIT" is the correct Linear team key for this project
3. Review enabled/disabled tools match team preferences for purple-stack
4. Check if PR title requirements format aligns with team standards

📋 Session info:

• Devin session: https://app.devin.ai/sessions/93ea9f59dac44eb0b184844c28e79877
• Requested by: jzemek@purple-technology.com (@zemeja)
• Related: Linear ticket AIT-27, reference implementation PTT-2623

[linear]

AIT-27 Add coderabbit instrumentation to sample repos

[devin-ai-integration]

🤖 Devin AI Engineer

I'll be helping with this pull request! Here's what you should know:

✅ I will automatically:

• Address comments on this PR. Add '(aside)' to your comment to have me ignore it.
• Look at CI failures and help fix them

Note: I can only respond to comments from users who have write access to this repository.

⚙️ Control Options:

• Disable automatic comment and CI monitoring