fix(install): build and select Linux musl release assets

[cb-muthiahm]

What changed

• Build and publish Linux x64 and arm64 musl release binaries alongside the five existing assets.
• Select musl or glibc in install.sh; explain missing Alpine runtime libraries before downloading.
• Bake the libc choice into Linux binaries so chargebee update downloads the matching asset.
• Run an Alpine install smoke in CI and document the libstdc++ and libgcc requirement.

Verification

• bun run typecheck
• bun run test:source (1353 pass, 0 fail)
• Built both musl targets with Bun 1.4.2.
• Installed the arm64 musl binary in a native Alpine 3.20 container and passed scripts/install-smoke-assert.sh.

The local x64 Alpine run under emulation stalled during binary startup; the new CI job runs x64 natively on Ubuntu. This PR is stacked on the installer verification PR (#15).

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[snyk-io]

✅ Snyk checks have passed. No issues have been found so far.

Status	Scan Engine	Critical	High	Medium	Low	Total (0)
✅	Open Source Security	0	0	0	0	0 issues
✅	Licenses	0	0	0	0	0 issues
✅	Code Security	0	0	0	0	0 issues

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[github-actions]

Test coverage

✅ Gate passed — all 77 files are at or above the 95% floor.

Status	Metric	Coverage	Threshold
✅	Functions	99.89%	95%
✅	Lines	99.52%	95%