fix(step-6): unset SAVED_TOKEN after self-test validation

Clears the read-back Telegram token from shell memory immediately after
the format-validation test, consistent with the unset pattern applied to
BOT_TOKEN/EXISTING_TOKEN in the installation block.

Author: fidgetcoding

step-6/step-6-install.sh

@@ -242,6 +242,7 @@ if [ -f "$TOKEN_FILE" ]; then
         echo -e "${RED}[FAIL]${NC} TEST: Token format invalid"
         TEST_FAIL=$((TEST_FAIL + 1))
     fi
+    unset SAVED_TOKEN
 else
     echo -e "${RED}[FAIL]${NC} TEST: Cannot validate token (file missing)"
     TEST_FAIL=$((TEST_FAIL + 1))