Fix GHCR workflow: upgrade Rust to 1.83, remove unsupported ARM v7

[Copilot]

GitHub Actions failing due to Rust version mismatch and unsupported platform architecture.

Changes

• Rust 1.81 → 1.83: askama 0.14.0 requires rustc 1.83+

  • Updated Dockerfile.build base image
  • Updated Cargo.toml rust-version

• Removed linux/arm/v7: rust:alpine only provides amd64/arm64 manifests

  • Removed from build matrix
  • Kept amd64 and arm64 support

• Fixed PR build flow: Conditionally skip digest export/upload for PRs

  • Prevents auth failures on pull request builds
  • Registry push remains main-branch only

Original prompt

#1

the github actions are failing

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