chore: mark US-013 as complete and update progress log

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

prd.json

@@ -227,7 +227,7 @@
         "Verify in browser using dev-browser skill"
       ],
       "priority": 13,
-      "passes": false,
+      "passes": true,
       "notes": ""
     },
     {

progress.txt

@@ -187,3 +187,20 @@
   - Hover effects on cards: border-blue-300, shadow-md, and text color change on title
   - Error state displayed if Supabase query fails
 ---
+
+## 2026-01-21 - US-013
+- What was implemented: Create new project functionality
+- Files changed:
+  - src/components/NewProjectButton.tsx - new client component with modal dialog
+  - src/app/dashboard/page.tsx - added NewProjectButton to header area
+  - src/app/signup/page.tsx - fixed lint error (setState in effect) by initializing email from searchParams
+- **Learnings for future iterations:**
+  - Modal dialogs use fixed positioning with backdrop (bg-black/50) for overlay effect
+  - Form submission uses Supabase insert with .select('id').single() to get the new record ID
+  - Initialize flowchart_data with { nodes: [], edges: [] } for new projects
+  - router.push() for programmatic navigation after successful creation
+  - autoFocus on input for better UX when modal opens
+  - Prevent modal close while loading (check isLoading before calling handleClose)
+  - ESLint rule react-hooks/set-state-in-effect warns against synchronous setState in useEffect
+  - Initialize state from searchParams directly in useState() instead of setting in useEffect
+---