Fix shared app-server socket DMG drift

[moxw]

Summary

• update the shared app-server socket detector for the current upstream SSH WebSocket transport class
• match the current local transport factory's WebSocket fallback block
• keep the patch fail-soft, idempotent, and latest-DMG-only
• add regression coverage that rejects the previous bundle shape

Root cause

The current DMG added fields before the SSH transport's kind marker and changed the local transport factory from a ternary fallback to an if (websocketUrl) block. The feature descriptor therefore skipped, and enabled-feature acceptance rejected the candidate.

User impact

Native bootstrap and updater rebuilds can accept the current DMG when shared-app-server-socket is enabled. The feature's runtime behavior is unchanged.

Validation

• node --test linux-features/shared-app-server-socket/test.js — 24 passed
• real current-DMG main bundle — first pass changed, second pass byte-identical, one transport injected
• node --check passed for the feature sources and patched current bundle
• current-DMG transactional rebuild — accepted_with_warnings; shared-app-server-socket applied once with no enabled-feature blockers

Limitations

The rebuild retains unrelated optional core drift warnings already present for the current DMG.

[ilysenko]

Reviewed the current head bd127c0. No blockers found; focused optional feature drift fix with passing checks.