release: publish DS Agent v1.5.0

[Lee-take]

Summary

• publish the exact v1.5.0 version, updater, installer, documentation, governance, and release-source surface
• document the production-reachable durable Computer Use lifecycle and its deliberately narrow installed-test boundary
• preserve all accepted Step 5 behavior and evidence contracts

Verified gates

• complete Rust: 1008 passed, 13 ignored, 0 failed
• all 19 Node suites; production build; format; 230-file secret scan; release-source; working/cached diff; migration and recovery
• fresh absolute-zero cargo clippy with warnings denied
• installed reliability: 30/30 exact Explorer/Excel/Edge-local-portal runs, 100% window recovery, 0 wrong-target writes, 0 false completions, plus 40 deterministic fault cases
• two fresh release builds reproduced exact installer and executable bytes
• extracted candidate passed isolated installed UI plus real Word artifact smoke without installing or mutating current DS Agent AppData

Candidate

DS.Agent_1.5.0_x64-setup.exe: 11,562,928 bytes; SHA-256 41a7165c7190703cbec281dff2a1ac100d0e61c497135ef9668586306181f3c5; version 1.5.0; Authenticode NotSigned.

This PR does not implement Step 6, enable production accounts or tenants, claim general browser control, reuse stored browser logins, or modify any existing tag, Release, or asset.