Add AUR publishing automation

[OneNoted]

What changed

• add reusable scripts to build release archives and render/publish AUR metadata
• add ghfetch-rs-bin and ghfetch-rs-git AUR package templates under packaging/aur
• add GitHub Actions to publish the -bin package on v* tags and refresh the -git package from main
• document the package names, release flow, and required AUR_SSH_PRIVATE_KEY secret in the README

Why

• ghfetch is already taken in the AUR, so this uses the ghfetch-rs-* names while still installing the ghfetch executable
• the release workflow should publish the prebuilt package from tagged artifacts and keep the VCS package current automatically
• CI should fail early if AUR metadata generation regresses

Validation

• cargo fmt --check
• cargo clippy --all-targets --all-features -- -D warnings
• cargo test
• local render of both AUR packages and the tagged release archive

[chatgpt-codex-connector]

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[chatgpt-codex-connector]

Align ghfetch-rs-git fallback pkgver with automation

When no v* tags are present, this pkgver() fallback hardcodes 0.0.0, but scripts/compute-git-pkgver.sh falls back to the Cargo version (0.1.0 here). The automation in .github/workflows/aur-git.yml renders and publishes metadata using the script output, so AUR metadata can advertise 0.1.0.r... while end users building the package get 0.0.0.r..., creating inconsistent versioning and confusing update behavior.

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