Support to linux zcode

[eltonacosta]

Summary

This PR fixes two Linux portability issues reported together:

1. Portable updater test archives (no more bsdtar)

The Linux test path shelled out to bsdtar to build fixture archives, but that binary is not a project dependency and isn't provisioned by CI. On a clean Linux environment without libarchive-tools, bun test failed with an executable-not-found error before exercising the updater. Both compress() helpers in tests/extension-updater.test.ts and tests/host-updater.test.ts now use a single in-process ZIP writer.

Changes:

• New tests/fixtures/archive.ts: an in-process ZIP builder (store/deflate, CRC32 table, UTF-8 filename flags, Unix mode attributes) with no external dependencies.
• tests/extension-updater.test.ts / tests/host-updater.test.ts: compress() delegates to writeZipFromDirectory(); bsdtar/Compress-Archive shell-outs removed on every platform.
• Added a round-trip test that extracts the generated fixture with the production reader (extractArchive/yauzl), so the fixture format stays honest.

2. Remove generated zcode.desktop on uninstall

When no desktop entry existed, readShortcut returned undefined, so installOrRepair stored no shortcut state — yet still created zcode.desktop. uninstall only restored state.shortcut, so a fresh Linux install left a broken launcher pointing at the deleted zdp-launcher.

Changes:

• src/cli/shortcut.ts: new captureShortcut() records created: true when no entry exists, and new removeLauncherShortcut() removes launcher-created entries, restores pre-existing ones, and safely handles legacy install states (matches the stored target against the launcher path) or missing state (skips non-launcher entries).
• src/cli/installer.ts: installOrRepair now always persists shortcut state (including created); uninstall delegates to removeLauncherShortcut() even when no state was recorded.
• src/shared/schemas.ts: shortcut schema accepts an empty originalTarget and the optional created flag; older states remain valid.

Tests (tests/installer.test.ts):

• Fresh install → generated .desktop removed on uninstall.
• Legacy state without shortcut data → generated entry still removed.
• Pre-existing entry → restored byte-for-byte on uninstall.
• Verified the new removal test fails against the pre-fix code (state.shortcut was undefined on fresh installs).

Verification

• bun run check passes fully: typecheck, 58 tests / 0 failures, SDK packaging check, example build, and host build.
• Real-machine doctor run confirms shortcutManaged: true with the existing install intact.

Files changed

File | Change -- | -- tests/fixtures/archive.ts | New in-process ZIP fixture writer tests/extension-updater.test.ts | Uses fixture writer; adds extraction round-trip test tests/host-updater.test.ts | Uses fixture writer src/cli/shortcut.ts | Shortcut capture/removal lifecycle (created tracking) src/cli/installer.ts | Persists shortcut state; uninstall removes generated entries src/shared/schemas.ts | Schema relaxations for generated-shortcut states tests/installer.test.ts | Fresh-install removal, legacy-state, and restore coverage