Add professional DevOps pipeline

[jasonmatthewsuhari]

Closes #4

Summary

Adds a professional DevOps baseline for Fluent:

• CI quality gates for typecheck, ESLint, JSX accessibility linting, Markdown linting, Prettier, production build, and high-severity production dependency audits.
• CodeQL, Dependency Review, OpenSSF Scorecard, and Dependabot.
• Nightly release workflow for unsigned pre-alpha Windows, macOS, and Linux artifacts.
• CodeRabbit configuration for assertive accessibility, automation safety, security, privacy, and workflow review.
• Development, DevOps, and release documentation.
• Missing src/styles.css so the app can actually build.

Verification

• npm run check
• npm run package
• npm run dist

Notes

CodeRabbit still needs the GitHub App enabled for the repository before reviews will run.
Nightly artifacts are unsigned and intended for testing only.

[github-advanced-security]

You are seeing this message because GitHub Code Scanning has recently been set up for this repository, or this pull request contains the workflow file for the Code Scanning tool.

What Enabling Code Scanning Means:

• The 'Security' tab will display more code scanning analysis results (e.g., for the default branch).
• Depending on your configuration and choice of analysis tool, future pull requests will be annotated with code scanning analysis results.
• You will be able to see the analysis results for the pull request's branch on this overview once the scans have completed and the checks have passed.

For more information about GitHub Code Scanning, check out the documentation.