Currency & naming overhaul

Renamed "Salvage" to "Scrap." Currency should feel tangible. You pick up scrap metal from dead things on an alien planet — that tracks. Existing saves migrate automatically.

Renamed "Spinal Column" to "The Conduit." The old name was too literal. The Conduit is the structure descending into the planet's core — a channel for the signal, not a spine.

Buffed Conduit rewards significantly. Scrap and XP now scale with depth, bosses give bonus rewards, and enhancement materials drop regularly with increasing chances the deeper you go. The Conduit should be THE place to farm materials.