Reasoning
Warcraft Tavern calls Tailoring 'undoubtedly the strongest profession for a Mage' since Mages wear cloth, and Forever gives every Mage specialization dedicated sets and pieces. Enchanting is the paired profession because it lets Mages self-enchant gear and, in Forever, has been expanded to also craft Staves, Totems, Idols, Librams, and Off-hands, plus new necklace enchants (Strength, Agility, Spell Power, Healing Power, Deflection). A second source independently confirms this exact Tailoring + Enchanting pairing for Mage with no PvE/PvP split noted. Source picks: Warcraft Tavern Mage guide: Tailoring + Enchanting; Koroboost (unverified): Tailoring + Enchanting.
Confidence note
Analysis built from sourced profession facts