How do we reconcile praying for specific worldly matters with being content with Allah's decree and seeking not to rely on one's self and its whims?

There is no contradiction between belief in divine decree (Qada' and Qadar) and supplicating for permissible things (mubahat). Supplication itself is part of divine decree, and it is an commanded act of worship. A person may supplicate for whatever they wish, even during prayer, as long as the supplication is not forbidden or obscene. This is indicated by the Hadith: "Then let him choose whatever supplication he wishes." And supplicating with "Do not leave me to myself even for the blink of an eye" does not contradict supplicating for permissible things that one desires. Rather, it is a delegation of affairs to Allah and reliance upon Him, and not a prohibition from asking Allah for the good and permissible things that one loves.