ci: use trusted Windows runner for manual E2E

[zpzjzj]

Summary

• route maintainer-dispatched Windows E2E and live-model checks to the trusted self-hosted Windows runner
• keep merge-group Windows code on ephemeral GitHub-hosted runners so persistent state cannot cross into later secret-bearing jobs
• verify Git for Windows, Git Bash, and symlink capability before running tests
• document runner labels, PATH, Developer Mode, persistence, and trust boundaries in English and Chinese
• use stock Windows PowerShell so PowerShell 7 is not an undocumented host prerequisite

Validation

• make verify
• make test
• actionlint .github/workflows/extended-ci.yml .github/workflows/model-e2e.yml
• Extended CI run 31768265668: Windows E2E passed on IZTW1IE30KF87BZ with 73 pass, 33 expected skip, 0 fail; the overall workflow failed only because an unrelated Linux Docker runner could not access /var/run/docker.sock
• Model E2E run 31768419858: Windows Claude token-usage test and artifact upload passed; readback reported 20,693 input and 25 output tokens

Security boundary

merge_group continues to select windows-2025. Only maintainer-authorized workflow_dispatch runs select [self-hosted, Windows, X64, trusted].

[JHWang-1997]

LGTM