feat: post-prestige automation (auto-adventurer) (#76)

## Summary

Closes #61

- Adds the **Autonomous Recruitment** prestige upgrade (50 runestones) to both the API and web data files
- Adds `autoAdventurer?: boolean` to the `GameState` type for backwards-compatible saves
- Adds tick-loop logic in GameContext that automatically purchases the highest-tier unlocked adventurer the player can afford each frame when the toggle is enabled
- Adds `toggleAutoAdventurer` callback and exposes it through the context
- Adds toggle UI in the Prestige Shop (mirrors the existing Auto-Prestige toggle pattern)
- Updates the How to Play guide in the About panel to document the new automation feature

✨ This issue was created with help from Hikari~ 🌸

Reviewed-on: #76
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

apps/api/src/data/prestigeUpgrades.ts

@@ -210,6 +210,15 @@ export const defaultPrestigeUpgrades: Array<PrestigeUpgrade> = [
     runestonesCost: 1200,
   },
   // ── Utility Unlocks ───────────────────────────────────────────────────────
+  {
+    category: "utility",
+    description:
+      "Unlock the Auto-Adventurer toggle. When enabled, the tick engine will automatically purchase the highest-tier adventurer you can currently afford.",
+    id:             "auto_adventurer",
+    multiplier:     1,
+    name:           "Autonomous Recruitment",
+    runestonesCost: 50,
+  },
   {
     category: "utility",
     description: