Bump VERSION to 0.12.0 for the next release

[onel]

Bumps the repo-root VERSION to 0.12.0 so the next dev -> main merge cuts the v0.12.0 release.

Step 1 of the release sequence in docs/dev/contributing.md # Cutting a release, step by step. No behaviour change.

Test plan

• VERSION reads 0.12.0.
• CI gates (ci-go, ci-web) on this PR.

[greptile-apps]

Confidence Score: 5/5

The PR appears safe to merge because the version bump matches the documented release process and all release artifacts derive from the root VERSION file.

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