feat: Add version discrepancy check to check-env script

[twk3]

Adds version discrepancy detection to help users identify when their .env file has an outdated image tag, and updates upgrade documentation to clarify that users must update DC_CURRENTS_IMAGE_TAG to pull new versions.

Changes

check-env.sh

• Compares DC_CURRENTS_IMAGE_TAG in .env with the VERSION file
• Shows a yellow warning if they differ, with upgrade instructions

docs/upgrading.md

• All three upgrade paths now explicitly mention updating DC_CURRENTS_IMAGE_TAG
• Added note explaining that the tag controls which version is pulled
• Referenced check-env.sh as a way to detect version discrepancies

Review hints

• The script change is in on-prem/scripts/check-env.sh around line 61-77
• Documentation changes add comments to existing code blocks and a callout note

Checklist

• PR title is Changelog-friendly: (fix|feat|chore): title [CSR-xxx]
• User-friendly and meaningful description of the changes
• Documentation was updated

---

Summary by cubic

Adds a version check to on-prem/scripts/check-env.sh to warn when your .env tag is outdated, and updates upgrading docs to make tag updates explicit. This helps prevent pulling the wrong image version.

• New Features
  • Compares DC_CURRENTS_IMAGE_TAG in .env to the VERSION file and shows a yellow warning if they differ.
  • Prints clear upgrade steps: update the tag, then run docker compose pull && docker compose up -d.

^{Written for commit 3131c28. Summary will update on new commits.}

[cubic-dev-ai]

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