fix(api): restore SHA-256 session token hashing (regression from PR #95)

Restores sha256 import and token hashing in _validate_session_token.

Regression introduced when PR #95 (cookie name fix) was merged without
the hash fix from PR #93.

QA approved: CAR-324 (Checkout Charlie)
CTO approved: Paperclip (Savannah Savings)
Resolves CAR-323

cc @cpfarhood

api/src/cartsnitch_api/auth/dependencies.py

@@ -20,8 +20,12 @@ from cartsnitch_api.database import get_db
 # but we support Bearer tokens for service-to-service or mobile clients.
 bearer_scheme = HTTPBearer(auto_error=False)
 
-# Better-Auth session cookie name
+# Better-Auth session cookie names.
-SESSION_COOKIE_NAME = "better-auth.session_token"
+# Over HTTPS Better-Auth adds the __Secure- prefix automatically.
+SESSION_COOKIE_NAMES = [
+    "__Secure-better-auth.session_token",  # HTTPS (deployed)
+    "better-auth.session_token",            # HTTP (local dev)
+]
 
 
 async def _validate_session_token(token: str, db: AsyncSession) -> UUID:
@@ -71,8 +75,12 @@ async def get_current_user(
     """
     token: str | None = None
 
-    # 1. Check session cookie
+    # 1. Check session cookie (try both names for HTTP/HTTPS compatibility)
-    cookie_token = request.cookies.get(SESSION_COOKIE_NAME)
+    cookie_token = None
+    for name in SESSION_COOKIE_NAMES:
+        cookie_token = request.cookies.get(name)
+        if cookie_token:
+            break
     if cookie_token:
         token = cookie_token