fix: report tag-driven release versions

[qartik]

Summary

• make actupdate version report an injected release version for published binaries, such as 0.2.0
• derive non-release version output from Go build metadata instead of a hardcoded dev
• build release artifacts when a GitHub release is published from a tag such as v0.2.0
• document using the GitHub new-release page and manual workflow reruns by tag

Details

Published release builds use the release tag as the source of truth and pass it through go build -ldflags, so binaries created from v0.2.0 report 0.2.0.

Non-release builds prefer Go module build metadata when available, including tagged versions or pseudo-versions, and fall back to an embedded devel-<commit> string from vcs.revision with +dirty when applicable. This avoids a bare dev version without querying git at runtime.

Validation

• go test ./...
• git diff --check
• GOCACHE=/private/tmp/go-cache-actupdate go run -ldflags "-X main.version=0.2.0" ./cmd/actupdate version
• GOCACHE=/private/tmp/go-cache-actupdate go build -o /private/tmp/actupdate-version-check ./cmd/actupdate && /private/tmp/actupdate-version-check version

[Copilot]

Pull request overview

This PR updates actupdate version to report meaningful versions for both published release binaries (via injected tag-derived versions) and local/source builds (via Go build metadata), and adjusts the release workflow/documentation accordingly.

Changes:

• Implement version display logic using -ldflags injection for releases and runtime/debug build info for non-release builds.
• Add unit tests covering injected versions and build-info-derived development versions.
• Update the GitHub release workflow to build from published release tags (and allow manual reruns by tag), plus update README release instructions.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
README.md	Updates release documentation to match tag-driven published-release builds and describe version reporting behavior.
cmd/actupdate/main.go	Replaces hardcoded version with injected/build-metadata-based displayVersion() logic.
cmd/actupdate/main_test.go	Adds tests for injected version output and debug.BuildInfo parsing behavior.
.github/workflows/release.yml	Triggers builds on published releases and injects tag-derived version via Go linker flags; adds manual dispatch input.

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