release: v1.15.0-rc.1 Agent workspace

[singchia]

Summary

• Prepare the v1.15.0-rc.1 prerelease with Codex and Claude Code integration, persistent conversations, file previews and timing diagnostics.
• Include upgrade/rollback guidance and explicit platform and interaction limitations.
• Add Claude, navigation and resilience regressions to CI; publish version-specific release notes.

Verification

• Full local Go build and race tests passed before release metadata changes.
• Isolated native Claude active interruption and exact-session resume passed.
• 24 browser locale/theme/viewport combinations passed for navigation, Claude interactions and resilience.
• Release version parser tests and shell syntax checks passed.

Tag and publish only after CI passes. This is a prerelease, not a stable release.