chore: ignore chalk major bumps until Node base reaches 22

[fank]

Summary

• Adds an ignore rule for chalk major version bumps in .github/dependabot.yml
• chalk 6+ requires Node >=22; this project currently targets Node 20 (.nvmrc) with engines ">=18.0.0"
• Closes chore(deps): bump chalk from 5.6.2 to 6.0.0 #109

Why

chalk 6.0.0 sets engines: { node: ">=22" }. Running on Node 20 is unsupported — CI only passed because npm doesn't enforce engines at install time, but code could break at runtime with any Node 22-specific API chalk 6 actually uses.

The ignore rule includes a comment to re-evaluate once the Node base is bumped to 22+.

Test plan

• CI passes (lint + format)
• dependabot.yml parses cleanly (Dependabot validates on push)

🤖 Generated with Claude Code

[gemini-code-assist]

Code Review

This pull request updates the Dependabot configuration in .github/dependabot.yml to ignore major version updates for the chalk dependency, as chalk v6 requires Node.js v22 or higher, whereas the project currently targets Node.js v20. There are no review comments, and I have no feedback to provide.