feat(server): Add readOnly mode to Cursor provider for read-only operations

Adds a readOnly option to ExecuteOptions that controls whether the
Cursor CLI runs with --force flag (allows edits) or without (suggest-only).

Read-only routes now pass readOnly: true:
- generate-spec.ts, generate-features-from-spec.ts (we write files ourselves)
- validate-issue.ts, generate-suggestions.ts (analysis only)
- describe-file.ts, describe-image.ts (description only)
- generate-plan.ts, enhance.ts (text generation only)

Routes that implement features (auto-mode-service, agent-service) keep
the default (readOnly: false) to allow file modifications.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

apps/server/src/routes/backlog-plan/generate-plan.ts

@@ -183,6 +183,7 @@ Please analyze the current backlog and the user's request, then provide a JSON p
       allowedTools: [], // No tools needed for this
       abortController,
       settingSources: autoLoadClaudeMd ? ['user', 'project'] : undefined,
+      readOnly: true, // Plan generation only generates text, doesn't write files
     });
 
     let responseText = '';