Snake Medallion quest redesigned — 7-scene desert run with Old Quarter walk

The old Snake Medallion quest was a 5-scene placeholder that ran from digsite-tents to medallion-recovered without much in between. It's now a 7-scene chain branching off broken-bridge: five battle scenes through the desert and old-digsite area, plus a new walking scene at the Old Quarter ruins.

The Old Quarter walking scene has a boulder-pickup trigger that gates the exit — you can't leave without finding the relic, so the quest can't finish in a weird half-state. Tara reads the snake glyph and gets teased for it; the Snake Order aside is fully scripted.

Quest opening, turn-in, and the Snake Order side scene are all in. Bark 17 carries the mid-quest line; bark 18 holds the post-completion follow-up.