feat: MVP-3 Sprint 2 - Auto tag suggestions, note connections panel

- Add auto tag suggestions to note form with debounced API calls
- Rename related notes to "También podrías necesitar" in detail view
- Create NoteConnections component showing backlinks, outgoing links, and related notes
- Add tests for backlinks module and tags/suggest API endpoint

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

__tests__/api.integration.test.ts

@@ -531,6 +531,64 @@ describe('API Integration Tests', () => {
     })
   })
 
+  // ============================================
+  // GET /api/tags/suggest - Suggest tags based on content
+  // ============================================
+  describe('GET /api/tags/suggest', () => {
+    it('suggests tags based on title keywords', async () => {
+      const { GET } = await import('@/app/api/tags/suggest/route')
+      const request = new NextRequest('http://localhost/api/tags/suggest?title=Docker%20deployment&content=')
+      const response = await GET(request)
+      const data = await response.json()
+
+      expect(response.status).toBe(200)
+      expect(data.success).toBe(true)
+      expect(Array.isArray(data.data)).toBe(true)
+    })
+
+    it('suggests tags based on content keywords', async () => {
+      const { GET } = await import('@/app/api/tags/suggest/route')
+      const request = new NextRequest('http://localhost/api/tags/suggest?title=&content=Docker%20and%20Kubernetes%20deployment')
+      const response = await GET(request)
+      const data = await response.json()
+
+      expect(response.status).toBe(200)
+      expect(data.success).toBe(true)
+      expect(Array.isArray(data.data))
+    })
+
+    it('combines title and content for suggestions', async () => {
+      const { GET } = await import('@/app/api/tags/suggest/route')
+      const request = new NextRequest('http://localhost/api/tags/suggest?title=Python%20script&content=SQL%20database%20query')
+      const response = await GET(request)
+      const data = await response.json()
+
+      expect(response.status).toBe(200)
+      expect(data.success).toBe(true)
+    })
+
+    it('returns empty array for generic content', async () => {
+      const { GET } = await import('@/app/api/tags/suggest/route')
+      const request = new NextRequest('http://localhost/api/tags/suggest?title=Note&content=content')
+      const response = await GET(request)
+      const data = await response.json()
+
+      expect(response.status).toBe(200)
+      expect(data.success).toBe(true)
+      expect(Array.isArray(data.data)).toBe(true)
+    })
+
+    it('handles empty parameters gracefully', async () => {
+      const { GET } = await import('@/app/api/tags/suggest/route')
+      const request = new NextRequest('http://localhost/api/tags/suggest')
+      const response = await GET(request)
+      const data = await response.json()
+
+      expect(response.status).toBe(200)
+      expect(data.success).toBe(true)
+    })
+  })
+
   // ============================================
   // GET /api/search - Search notes
   // ============================================