Add simple auth

README.md

@@ -9,14 +9,20 @@ AI-generated cross-book summaries, and engage in grounded RAG chat.
 ```mermaid
 graph TD
     User["Neurosurgeon (Browser)"]
+    Login["Login Page\n(username + password form)"]
     FE["Frontend\nVue.js 3 / Vite\n:5173"]
     BE["Backend\nSpring Boot 4 / Spring AI\n:8080"]
+    Auth["Spring Security\nHTTP Basic Auth"]
     DB["PostgreSQL + pgvector\n(source of truth)"]
     FS["File Store\nuploads/ (local disk)\nExtracted figure PNGs"]
     LLM["LLM Provider\n(OpenAI)\nEmbeddings + Chat + Vision"]
 
-    User -->|HTTP| FE
-    FE -->|REST /api/v1/...| BE
+    User -->|"First visit / unauthenticated"| Login
+    Login -->|"POST credentials\n(GET /api/v1/auth/check)"| Auth
+    Auth -->|"401 → back to login\n200 → app access"| Login
+    Login -->|"Authenticated"| FE
+    FE -->|"REST /api/v1/...\n(HTTP Basic on every request)"| Auth
+    Auth --> BE
     BE -->|"JDBC — books, chapters,\nsections, figures, refs"| DB
     BE -->|"pgvector — text chunks\n+ figure caption vectors"| DB
     BE -->|"PNG read/write\n(figure extraction)"| FS