Fix Linux installer for musl systems

[robinbraemer]

Summary

• add musl-tagged Linux release artifacts (gate_<version>_linux_<arch>_musl) via GoReleaser
• make the Unix installer skip asset-less releases, use fail-fast downloads, verify staged binaries, and select _musl assets on Alpine/musl
• add musl build fallbacks that omit native GeyserLite and Honeycomb otel-config dependencies so the musl binary is statically linked
• document the musl binary tradeoffs and add installer/build-tag regression tests

Musl build caveat

The musl binary intentionally excludes native GeyserLite managed mode and Honeycomb OpenTelemetry auto-configuration because those paths currently pull in purego/libdl. Managed Bedrock on musl should use bedrock.managed.engine: java; users needing native GeyserLite or full OTEL support should use the standard glibc build or Docker image.

Verification

• make test
• go run github.com/goreleaser/goreleaser/v2@latest check
• go run github.com/goreleaser/goreleaser/v2@latest release --snapshot --clean --skip=publish
• GOOS=linux GOARCH=amd64 CGO_ENABLED=0 go build -tags musl -ldflags="-s -w" -o /tmp/gate_linux_amd64_musl_check gate.go produced a statically linked ELF

[cloudflare-workers-and-pages]

Deploying gate-minekube with    Cloudflare Pages

Latest commit:	e22541c
Status:	✅  Deploy successful!
Preview URL:	https://0731200c.gate-minekube.pages.dev
Branch Preview URL:	https://codex-fix-linux-installer-mu.gate-minekube.pages.dev

View logs