feat: two-step issue resolution (resolve then delete)

- New PATCH /issues/{id} endpoint to toggle resolved flag
- Add resolved:false to new issues
- Frontend: click "✓ Resolve" marks issue green with strikethrough
- Resolved issues show "↺ Reopen" and "🗑 Delete" buttons
- Delete requires confirmation
- Sort: unresolved first, then resolved
- Issues persist until explicitly deleted

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

main.py

@@ -1368,6 +1368,7 @@ async def add_issue(issue: dict):
         "category": issue.get("category", "other"),
         "author": issue.get("author", "Anonymous").strip(),
         "created": datetime.utcnow().isoformat(),
+        "resolved": False,
     }
     if not new_issue["title"]:
         raise HTTPException(status_code=400, detail="Title is required")
@@ -1376,9 +1377,26 @@ async def add_issue(issue: dict):
     return new_issue
 
 
+@app.patch("/issues/{issue_id}")
+async def update_issue(issue_id: str, update: dict):
+    """Update an issue (e.g. toggle resolved state)."""
+    issues = _load_issues()
+    found = None
+    for i in issues:
+        if i.get("id") == issue_id:
+            if "resolved" in update:
+                i["resolved"] = bool(update["resolved"])
+            found = i
+            break
+    if not found:
+        raise HTTPException(status_code=404, detail="Issue not found")
+    _save_issues(issues)
+    return found
+
+
 @app.delete("/issues/{issue_id}")
 async def delete_issue(issue_id: str):
-    """Resolve (delete) an issue."""
+    """Permanently delete an issue."""
     issues = _load_issues()
     issues = [i for i in issues if i.get("id") != issue_id]
     _save_issues(issues)