fix(upgrade): improve failure diagnostics

[GatewayJ]

Summary

• classify common upgrade failures such as network, HTTP status, disk space, permission, missing path, and invalid archive errors
• persist structured upgrade failure metadata and log path separately from the raw error text
• render localized upgrade failure guidance in the modal and sidebar, including long log paths in light and dark themes
• add regression coverage for backend classification, API propagation, CLI output, and frontend formatting

Root cause

The upgrade helper previously surfaced the raw download/write error directly, so stream/network failures and local filesystem problems were hard to distinguish. The log path was appended into the raw message instead of being exposed as structured status.

Validation

• go test ./...
• pnpm --dir web/app test -- upgradeStatus useUpgradeController UpgradeModal SidebarUserButton
• pnpm --dir web/app typecheck
• pnpm --dir web/app format:check
• pnpm --dir web/app lint
• git diff --check