ci: harden dependency restore and token defaults

[EricSun0218]

Summary

• enforce NuGet lock files in both ordinary and trusted .NET restore gates
• default the privileged trusted workflow token to no permissions, preserving only explicit per-job grants
• remove two timing races exposed by simultaneous Windows/Linux CI: wait for the intended deadline stage and for detached-provider cleanup accounting
• use GitHub-signed and verified commits so the protected branch never needs an administrator bypass

Verification

• Release version consistency check and self-test
• Trusted workflow contract self-test
• locked-mode solution restore
• focused race tests: 20/20 repeated rounds passed
• complete persistence suite: 511/511 passed
• solution formatting verification passed
• full GitHub CI, engines, CodeQL, dependencies, and trusted artifact matrix required before auto-merge