Linting: Prefer optional chaining

[henrymercer]

🚲🏠

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Merge / deployment checklist

• Confirm this change is backwards compatible with existing workflows.
• Consider adding a changelog entry for this change.
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[Copilot]

Pull Request Overview

This PR applies a linting rule to enforce the use of optional chaining (?.) instead of manual null/undefined checks combined with property access. The changes simplify conditional expressions by replacing patterns like foo && foo.bar and foo === null || foo.bar with the more concise foo?.bar syntax.

Key changes:

• Enabled the @typescript-eslint/prefer-optional-chain ESLint rule
• Refactored conditional expressions throughout the codebase to use optional chaining
• Updated both TypeScript source files and their compiled JavaScript outputs

Reviewed Changes

Copilot reviewed 14 out of 14 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
eslint.config.mjs	Enabled the @typescript-eslint/prefer-optional-chain linting rule
src/workflow.ts	Simplified undefined check with optional chaining for input validation
src/tar.ts	Applied optional chaining to regex match result checks
src/start-proxy-action-post.ts	Refactored config debug mode check using optional chaining
src/setup-codeql.ts	Simplified null check with optional chaining for match result
src/config/db-config.ts	Consolidated nested property checks into single optional chaining expression
src/config-utils.ts	Applied optional chaining to regex match groups check
lib/*.js	Compiled JavaScript output reflecting the TypeScript changes above

[mbg]

Not a huge fan of the ?.[i] case, but otherwise I am in favour of this change, so I'll approve.