feat(FN-794): raise auto-summarization threshold from 140 to 200 characters

- Change MIN_DESCRIPTION_LENGTH threshold from 140 to 200 in ai-summarize.ts
- Update shouldAutoSummarize logic and tests for new 200-char threshold
- Update UI copy in SettingsModal and API/routes references
- Update store tests to reflect the new threshold value
- Remove obsolete dashboard activity-log mobile layout test files and unused CSS
- Add changeset for patch bump

packages/core/src/store.ts

@@ -672,7 +672,7 @@ export class TaskStore extends EventEmitter<TaskStoreEvents> {
     let title = input.title?.trim() || undefined;
     const shouldSummarize =
       !title && // Only if no title provided
-      input.description.length > 140 && // Only if description is long enough
+      input.description.length > 200 && // Only if description is long enough
       (input.summarize === true || // Explicit request
         options?.settings?.autoSummarizeTitles === true); // Auto-enabled