Upgrade notification silently skipped — users never see update indicator

[anandgupta42]

Problem

Users on older versions (e.g., 0.5.2) never see the upgrade indicator or toast notification when a newer version (e.g., 0.5.7) is available. The footer just shows the current version number with no upgrade prompt.

Root Cause

The upgrade() function in packages/opencode/src/cli/upgrade.ts silently returns without publishing any event in several scenarios:

1. autoupdate: false or OPENCODE_DISABLE_AUTOUPDATE=true — returns with no notification at all
2. Install method is "unknown" — returns with no notification
3. Auto-upgrade fails — .catch(() => {}) swallows the error silently
4. yarn install method — detected by method() but not in Installation.upgrade() switch, throws, caught silently

Additionally, there is no semver guard against downgrading canary/preview users to an older stable release.

Expected Behavior

The upgrade indicator (↑ 0.5.7 update available · altimate upgrade) should always appear in the TUI footer when a newer version exists, regardless of the autoupdate setting. The autoupdate config should only control whether the upgrade happens automatically, not whether the user is informed.

Screenshots

Before (bug): v0.5.2 with no upgrade indicator despite 0.5.7 being available
After (fix): Upgrade indicator shown in footer