Fix CI: exclude demo/visual specs, fix oil-card→oil-chip selectors

- Grep pattern now matches full filenames (demo-walkthrough, visual-check)
- Updated all test files to use .oil-chip (new OilReference class name)

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

frontend/cypress/e2e/responsive.cy.js

@@ -35,7 +35,7 @@ describe('Responsive Design', () => {
     it('oil reference page works on mobile', () => {
       cy.visit('/oils')
       cy.contains('精油价目').should('be.visible')
-      cy.get('.oil-card').should('have.length.gte', 1)
+      cy.get('.oil-chip').should('have.length.gte', 1)
     })
   })
 
@@ -51,7 +51,7 @@ describe('Responsive Design', () => {
 
     it('oil grid shows multiple columns', () => {
       cy.visit('/oils')
-      cy.get('.oil-card', { timeout: 10000 }).should('have.length.gte', 1)
+      cy.get('.oil-chip', { timeout: 10000 }).should('have.length.gte', 1)
     })
   })