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/e2e/global.setup.ts

@@ -37,7 +37,17 @@ setup("seed + authenticate", async ({ page }) => {
     try {
       const out = execFileSync(
         "docker",
-        ["exec", "-i", "-e", `E2E_EMAIL=${EMAIL}`, "-e", `E2E_PASSWORD=${PASSWORD}`, CONTAINER, "python", "-"],
+        [
+          "exec",
+          "-i",
+          "-e",
+          `E2E_EMAIL=${EMAIL}`,
+          "-e",
+          `E2E_PASSWORD=${PASSWORD}`,
+          CONTAINER,
+          "python",
+          "-",
+        ],
         { input: readFileSync(SEED_SCRIPT) },
       );
       console.log(`[e2e seed] ${out.toString().trim()}`);