add backend auth

backend/internal/db/migrations/010_auth.up.sql

@@ -0,0 +1,19 @@
+CREATE TABLE users (
+  id            TEXT PRIMARY KEY DEFAULT gen_random_uuid(),
+  username      TEXT NOT NULL UNIQUE,
+  password_hash TEXT NOT NULL,
+  created_at    TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP,
+  updated_at    TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE TABLE refresh_tokens (
+  id         TEXT NOT NULL DEFAULT gen_random_uuid(),
+  user_id    TEXT NOT NULL REFERENCES users(id) ON DELETE CASCADE,
+  token_hash TEXT NOT NULL,
+  expires_at TIMESTAMP NOT NULL,
+  revoked    BOOLEAN NOT NULL DEFAULT FALSE,
+  created_at TIMESTAMP NOT NULL DEFAULT CURRENT_TIMESTAMP
+);
+
+CREATE INDEX idx_refresh_tokens_user_id ON refresh_tokens(user_id);
+CREATE INDEX idx_refresh_tokens_token_hash ON refresh_tokens(token_hash);