fix(release): stabilize native sandbox proxy readiness

[killswitch-GUI]

Summary

• retry the authenticated proxy readiness probe on transient connection-refused results
• prepare version 0.10.10-preview.5 across Rust, Desktop, and fuzz manifests and lockfiles
• document that preview.5 supersedes the unpublished preview.4 attempt

Validation

• cargo xtask check rust
• cargo xtask pr --base origin/main
• ./release/verify-release-readiness.sh
• native sandbox release acceptance passed seven local executions, including the full gates

Release context

The v0.10.10-preview.4 tag workflow failed twice before draft creation because the macOS ARM runner reached the authenticated loopback proxy before it accepted connections. The retry is bounded to the allowed proxy probe; the raw-egress denial assertion is unchanged.

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