Expand test suite to 364 tests (168 unit + 196 E2E)

Unit tests:
- Volume/dilution calculation (63 tests): scaling, mode detection,
  ratio calculation, real recipe round-trip verification

E2E tests:
- Batch operations: create/tag/delete 3 recipes, adopt workflow
- Projects: CRUD, pricing, profit calculation vs oil costs
- Notifications: fetch, fields, mark-all-read
- Account settings: profile read/update, auth rejection
- Category modules: listing, tag reference
- Registration: register, login, duplicate rejection
- Audit log: pagination, field validation, action tracking

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

frontend/cypress/e2e/projects-flow.cy.js

@@ -0,0 +1,85 @@
+describe('Projects Flow', () => {
+  const ADMIN_TOKEN = 'c86ae7afbe10fabe3c1d5e1a7fee74feaadfd5dc7be2ab62'
+  const authHeaders = { Authorization: `Bearer ${ADMIN_TOKEN}` }
+  let testProjectId = null
+
+  it('creates a project', () => {
+    cy.request({
+      method: 'POST', url: '/api/projects', headers: authHeaders,
+      body: {
+        name: 'Cypress测试项目',
+        ingredients: JSON.stringify([{ oil: '薰衣草', drops: 5 }, { oil: '乳香', drops: 3 }]),
+        pricing: 100,
+        note: 'E2E test project'
+      }
+    }).then(res => {
+      expect(res.status).to.be.oneOf([200, 201])
+      testProjectId = res.body.id
+    })
+  })
+
+  it('lists projects', () => {
+    cy.request({ url: '/api/projects', headers: authHeaders }).then(res => {
+      expect(res.body).to.be.an('array')
+      const found = res.body.find(p => p.name === 'Cypress测试项目')
+      expect(found).to.exist
+      testProjectId = found.id
+    })
+  })
+
+  it('updates the project pricing', () => {
+    cy.request({ url: '/api/projects', headers: authHeaders }).then(res => {
+      const found = res.body.find(p => p.name === 'Cypress测试项目')
+      testProjectId = found.id
+      cy.request({
+        method: 'PUT', url: `/api/projects/${testProjectId}`, headers: authHeaders,
+        body: { pricing: 200, note: 'updated pricing' }
+      }).then(r => expect(r.status).to.eq(200))
+    })
+  })
+
+  it('verifies update', () => {
+    cy.request({ url: '/api/projects', headers: authHeaders }).then(res => {
+      const found = res.body.find(p => p.name === 'Cypress测试项目')
+      expect(found.pricing).to.eq(200)
+    })
+  })
+
+  it('project profit calculation is correct', () => {
+    // Fetch oils to calculate expected cost
+    cy.request('/api/oils').then(oilRes => {
+      const oilMap = {}
+      oilRes.body.forEach(o => { oilMap[o.name] = o.bottle_price / o.drop_count })
+
+      cy.request({ url: '/api/projects', headers: authHeaders }).then(res => {
+        const proj = res.body.find(p => p.name === 'Cypress测试项目')
+        const ings = JSON.parse(proj.ingredients)
+        const cost = ings.reduce((s, i) => s + (oilMap[i.oil] || 0) * i.drops, 0)
+        const profit = proj.pricing - cost
+        expect(profit).to.be.gt(0) // pricing(200) > cost
+        expect(cost).to.be.gt(0)
+      })
+    })
+  })
+
+  it('deletes the project', () => {
+    cy.request({ url: '/api/projects', headers: authHeaders }).then(res => {
+      const found = res.body.find(p => p.name === 'Cypress测试项目')
+      if (found) {
+        cy.request({
+          method: 'DELETE', url: `/api/projects/${found.id}`, headers: authHeaders
+        }).then(r => expect(r.status).to.eq(200))
+      }
+    })
+  })
+
+  after(() => {
+    cy.request({ url: '/api/projects', headers: authHeaders, failOnStatusCode: false }).then(res => {
+      if (res.status === 200 && Array.isArray(res.body)) {
+        res.body.filter(p => p.name && p.name.includes('Cypress')).forEach(p => {
+          cy.request({ method: 'DELETE', url: `/api/projects/${p.id}`, headers: authHeaders, failOnStatusCode: false })
+        })
+      }
+    })
+  })
+})