fix(app): handle session.error events in global sync

[CannonRS]

Issue for this PR

Closes #48530

Type of change

• Bug fix
• New feature
• Refactor / code improvement
• Documentation

What does this PR do?

The global sync reducer now handles session.error events instead of ignoring them. When a session turn fails, the reducer resets the session status to idle and marks the last assistant message with an error and finish: "error". A new optional notifyError callback is threaded into applyDirectoryEvent; the server-sync layer uses it to show a toast with the error message (reusing the existing notification.session.error.* i18n keys).

How did you verify your code works?

• bun typecheck (tsgo) passes in packages/app.
• event-reducer.test.ts passes 17/17, including a new test asserting the status reset and assistant error marker on session.error.
• git diff --check clean; no unrelated changes.

Screenshots / recordings

n/a (server/state behaviour; the toast is the only UI, using existing keys)

Fork

• Source fork: https://github.com/mQorva/OpenCode
• Diff against this fork's dev: mQorva/OpenCode@dev...session-error-sync
• mQorva issue / context: n/a

Checklist

• I have tested my changes locally
• I have not included unrelated changes in this PR