Merge the single and multi strategy panels into one

The single "Strategy" panel and "Strategies (multi)" were redundant: the multi
panel with one row is exactly the single-strategy behaviour. Remove StrategyPanel
and make "Strategies" the one trading panel. Presets move into it (load adds a
row, per-row Save), and the header now reports "N strategies" when several run
instead of only the first. Deletes the obsolete component and its test; adds
preset tests to the multi-strategy suite.

frontend/src/multi-strategy.test.js

@@ -1,7 +1,11 @@
 import { mount } from '@vue/test-utils'
-import { describe, expect, it } from 'vitest'
+import { afterEach, describe, expect, it, vi } from 'vitest'
 import MultiStrategyPanel from './components/MultiStrategyPanel.vue'
 
+afterEach(() => {
+  vi.restoreAllMocks()
+})
+
 const STRATEGIES = [
   {
     key: 'sma_cross',
@@ -19,9 +23,20 @@ const STRATEGIES = [
 
 const EMPTY_STATUS = { running: false, strategies: [], total_pnl: 0, equity: 0 }
 
-function mountPanel(multiStatus = EMPTY_STATUS) {
+const PRESETS = [
+  {
+    id: 1,
+    name: 'BTC fast',
+    strategy_key: 'ema_cross',
+    symbol: 'ETH/USDT',
+    timeframe: '15m',
+    params: { fast: 3 },
+  },
+]
+
+function mountPanel(multiStatus = EMPTY_STATUS, presets = []) {
   return mount(MultiStrategyPanel, {
-    props: { strategies: STRATEGIES, multiStatus, busy: false, loading: false },
+    props: { strategies: STRATEGIES, multiStatus, presets, busy: false, loading: false },
   })
 }
 
@@ -89,6 +104,39 @@ describe('MultiStrategyPanel', () => {
     expect(text).toContain('running')
   })
 
+  it('loads a preset as an additional row', async () => {
+    const wrapper = mountPanel(EMPTY_STATUS, PRESETS)
+    const presetSelect = wrapper.findAll('select').find((s) => s.text().includes('BTC fast'))
+    expect(presetSelect).toBeTruthy()
+
+    await presetSelect.setValue('1')
+
+    // A second row now exists, seeded from the preset.
+    expect(wrapper.findAll('select').length).toBeGreaterThan(1)
+    const inputs = wrapper.findAll('input')
+    expect(inputs.some((i) => i.element.value === 'ETH/USDT')).toBe(true)
+    expect(inputs.some((i) => i.element.value === '15m')).toBe(true)
+  })
+
+  it('emits save-preset with the row config', async () => {
+    vi.spyOn(window, 'prompt').mockReturnValue('my preset')
+    const wrapper = mountPanel()
+    const save = wrapper.findAll('button').find((b) => b.text() === 'Save')
+    await save.trigger('click')
+    const payload = wrapper.emitted('save-preset')[0][0]
+    expect(payload.name).toBe('my preset')
+    expect(payload.strategy_key).toBe('sma_cross')
+    expect(payload.params).toEqual({ fast: 10 })
+  })
+
+  it('does not save when the prompt is cancelled', async () => {
+    vi.spyOn(window, 'prompt').mockReturnValue(null)
+    const wrapper = mountPanel()
+    const save = wrapper.findAll('button').find((b) => b.text() === 'Save')
+    await save.trigger('click')
+    expect(wrapper.emitted('save-preset')).toBeUndefined()
+  })
+
   it('marks a halted strategy', () => {
     const wrapper = mountPanel({
       running: true,