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/dashboard/app/components/SettingsModal.tsx

@@ -991,7 +991,7 @@ export function SettingsModal({
                 Auto-summarize long descriptions as titles
               </label>
               <small>
-                When enabled, tasks created without a title but with descriptions over 140 characters
+                When enabled, tasks created without a title but with descriptions over 200 characters
                 will automatically get an AI-generated title (max 60 characters).
               </small>
             </div>