style(frontend): Prettier config + one-time repo-wide format pass

Prettier 3 (pinned), printWidth 100, double quotes — chosen to match the existing
hand-formatting and minimise reflow. This commit is ONLY the mechanical format pass
(`prettier --write`) plus the config/ignore/scripts, isolated so it never pollutes a
feature diff. Verified behaviour-neutral: typecheck, eslint (0 errors), and vitest
all green before and after. See .git-blame-ignore-revs — `git blame` skips this sha.

frontend/src/components/tableHeader.tsx

@@ -17,8 +17,16 @@ import { type SortState } from "../lib/columnSort";
 
 type ColumnFilter<T> =
   | { kind: "text"; get: (row: T) => string }
-  | { kind: "select"; options: { value: string; label: string }[]; test: (row: T, value: string) => boolean }
-  | { kind: "multi"; options: { value: string; label: string }[]; test: (row: T, values: string[]) => boolean };
+  | {
+      kind: "select";
+      options: { value: string; label: string }[];
+      test: (row: T, value: string) => boolean;
+    }
+  | {
+      kind: "multi";
+      options: { value: string; label: string }[];
+      test: (row: T, values: string[]) => boolean;
+    };
 
 export interface Column<T> {
   key: string;
@@ -55,7 +63,7 @@ export function filterRows<T>(rows: T[], columns: Column<T>[], filters: FilterMa
       if (f.kind === "text") return f.get(row).toLowerCase().includes(String(val).toLowerCase());
       if (f.kind === "select") return f.test(row, String(val));
       return f.test(row, val as string[]);
-    })
+    }),
   );
 }
 
@@ -247,13 +255,13 @@ export function ColumnHead<T>({
                     className="inline-flex items-center gap-1 hover:text-fg cursor-pointer"
                   >
                     {col.header}
-                    {isSorted && sort && (
-                      sort.dir === "asc" ? (
+                    {isSorted &&
+                      sort &&
+                      (sort.dir === "asc" ? (
                         <ArrowUp className="w-3 h-3" />
                       ) : (
                         <ArrowDown className="w-3 h-3" />
-                      )
-                    )}
+                      ))}
                   </button>
                 ) : (
                   <span>{col.header}</span>