Retry the strategy list and make collapse obvious

- The strategy/preset lists were loaded once with failures swallowed, so a
  single failed first request left the strategy dropdown empty forever. They
  are now retried every 3s until populated.
- Clearer collapse affordance: hover highlight, a hide/show hint, and a
  tooltip; Backtest and Parameter sweep start collapsed so the strategy
  selector and status are immediately visible.
- Adds an integration test that the strategy dropdown is populated and the
  panel actually collapses.

frontend/src/strategy-panel.test.js

@@ -0,0 +1,48 @@
+import { mount } from '@vue/test-utils'
+import { describe, expect, it } from 'vitest'
+import StrategyPanel from './components/StrategyPanel.vue'
+
+function mountPanel() {
+  return mount(StrategyPanel, {
+    props: {
+      strategies: [
+        {
+          key: 'sma_cross',
+          name: 'SMA Crossover',
+          description: 'test',
+          params: [{ name: 'fast', type: 'int', default: 10, description: '' }],
+        },
+      ],
+      status: { running: false, symbol: 'BTC/USDT', timeframe: '5m', open_positions: 0 },
+      busy: false,
+      presets: [],
+    },
+  })
+}
+
+describe('StrategyPanel collapse', () => {
+  it('shows the strategy form by default', () => {
+    const wrapper = mountPanel()
+    expect(wrapper.find('select').exists()).toBe(true)
+  })
+
+  it('hides the form when the header is clicked', async () => {
+    const wrapper = mountPanel()
+    const header = wrapper.find('button')
+    expect(header.attributes('aria-expanded')).toBe('true')
+
+    await header.trigger('click')
+
+    expect(wrapper.find('button').attributes('aria-expanded')).toBe('false')
+    // The form container is v-show-hidden, so the select is no longer visible.
+    const hidden = wrapper.findAll('div').some((d) => d.element.style.display === 'none')
+    expect(hidden).toBe(true)
+  })
+
+  it('picks the first strategy so the dropdown is populated', () => {
+    const wrapper = mountPanel()
+    const select = wrapper.find('select')
+    expect(select.element.value).toBe('sma_cross')
+    expect(select.findAll('option')).toHaveLength(1)
+  })
+})