fix(artifacts): parse Docker ENV assignment lists

[MikeeI]

Summary

Parse Docker ENV and ARG directives as logical instructions rather than isolated physical lines.
Preserve every valid assignment without evaluating build-time variables.

Evidence

• Current parsing stops at the first equals sign.
• Docker permits multiple assignment pairs and escaped continuations.

Changes

• Fold continued Dockerfile instructions.
• Tokenize modern, legacy, and bare directive forms with quote and escape handling.

Risks and boundaries

• Variable references remain symbolic and are not interpolated.
• A full Dockerfile parser and new dependency remain out of scope.

Verification

• bun test test/config-keys.test.ts
• bun test
• bun run typecheck

I checked the relevant issues, comments, pull requests, and discussions; this pull request is not a duplicate.

Disclosure

Investigated thoroughly with GPT-5.6 at extra-high reasoning effort.
I used Oh My Pi as the agent framework.
This report is not generic or unreviewed AI-generated output.
Its claims were checked against the cited evidence.
It includes the relevant detail intended to help maintainers resolve the issue.
If reports like this are not useful to the project, please let me know.
I will refrain from submitting similar reports.
My intent is to help without wasting maintainer time or energy or discouraging their work.
Thank you for your work.