fix(workspaces): surface invalid OpenCode configuration (#635)

## Summary
- validate the authenticated OpenCode process configuration before
publishing a workspace as ready
- stop and remove instances that report invalid configuration
- show localized configuration diagnostics, affected paths, validation
issues, and typo suggestions in the existing launch-error dialog

## Existing coverage
PR #195 already handles binary spawn and early-exit failures. PR #582
surfaces session-list loading failures. This change closes the remaining
case where OpenCode reports healthy while configuration-dependent
endpoints fail.

## Validation
- `bun test ./packages/server/src/workspaces/manager.test.ts`
- `node --import tsx --test packages/ui/src/lib/launch-errors.test.ts`
- server and UI typechecks
- UI build
- manual reproduction with OpenCode 1.18.5
- independent Gatekeeper reviews: PASS

Closes #508

.github/workflows/pr-build.yml

@@ -107,6 +107,7 @@ jobs:
           packages/ui/src/components/session-list-visibility.test.ts
           packages/ui/src/components/unified-picker-path.test.ts
           packages/ui/src/lib/hooks/use-app-session-capture.test.ts
+          packages/ui/src/lib/launch-errors.test.ts
           packages/ui/src/lib/message-selection-position.test.ts
           packages/ui/src/lib/trailing-resync.test.ts
           packages/ui/src/stores/abort-created-workspace-cleanup.test.ts