feat(client): add Timestamp component, ESLint 10 + Prettier, and code quality fixes

- add Timestamp component with moment relative time and ISO tooltip
- add Timestamp stories (JustNow, MinutesAgo, HoursAgo, DaysAgo, MonthsAgo)
- add ESLint 10 with typescript-eslint, react-hooks, react-refresh, prettier
- add Prettier config with singleQuote, semi, trailingComma all, printWidth 100
- add lint, lint:fix, format, test:storybook scripts to package.json
- fix react-hooks/set-state-in-effect in all page components
- auto-fix 113 Prettier formatting issues across src and .storybook

client/.storybook/stories/Timestamp.stories.tsx

@@ -0,0 +1,21 @@
+import type { Meta, StoryObj } from '@storybook/react-vite';
+import { Timestamp } from '../../src/ui/Timestamp/Timestamp';
+
+const meta: Meta<typeof Timestamp> = {
+  title: 'UI/Timestamp',
+  component: Timestamp,
+  parameters: { layout: 'centered' },
+  tags: ['autodocs'],
+};
+export default meta;
+type Story = StoryObj<typeof Timestamp>;
+
+const minutesAgo = (n: number) => new Date(Date.now() - n * 60_000).toISOString();
+const hoursAgo = (n: number) => new Date(Date.now() - n * 3_600_000).toISOString();
+const daysAgo = (n: number) => new Date(Date.now() - n * 86_400_000).toISOString();
+
+export const JustNow: Story = { args: { value: minutesAgo(1) } };
+export const MinutesAgo: Story = { args: { value: minutesAgo(15) } };
+export const HoursAgo: Story = { args: { value: hoursAgo(3) } };
+export const DaysAgo: Story = { args: { value: daysAgo(5) } };
+export const MonthsAgo: Story = { args: { value: daysAgo(90) } };