feat: enforce mandatory rationale and role in explore/diagnosis schema output

- Remove oneOf string option from relevant_files/affected_files, require structured objects
- Add required fields: rationale (minLength 10), role/change_type enum
- Add optional fields: discovery_source, key_symbols
- Update all caller commands with new format instructions and success criteria
- Fix consumer code: Map-based dedup, getPath() helper, path extraction
- Fix frontend: f.rationale || f.reason backward-compatible fallback

ccw/src/templates/dashboard-js/views/lite-tasks.js

@@ -954,7 +954,7 @@ function renderMultiCliContextContent(context, session) {
               <li class="file-item">
                 <span class="file-icon">📄</span>
                 <code>${escapeHtml(typeof f === 'string' ? f : f.path || f.file || '')}</code>
-                ${f.reason ? `<span class="file-reason">${escapeHtml(f.reason)}</span>` : ''}
+                ${(f.rationale || f.reason) ? `<span class="file-reason">${escapeHtml(f.rationale || f.reason)}</span>` : ''}
               </li>
             `).join('')}
           </ul>