fix: preserve boss first-kill state across prestige

Fixes #39. Added bountyRunestonesClaimed?: boolean to the Boss type.
The first-kill bounty runestones are now only awarded once across all
prestige resets — the boss route checks the flag before awarding, sets
it on first defeat, and buildPostPrestigeState carries the flag forward
through fresh boss state on prestige. The boss panel badge no longer
shows for bosses whose bounty has already been claimed.

packages/types/src/interfaces/boss.ts

@@ -59,6 +59,13 @@ interface Boss {
    * One-time runestone bounty awarded on first-ever defeat.
    */
   bountyRunestones: number;
+
+  /**
+   * Whether the first-kill runestone bounty has already been claimed.
+   * Set to true on first defeat and preserved across all prestiges so the
+   * bounty is never re-awarded in subsequent runs.
+   */
+  bountyRunestonesClaimed?: boolean;
 }
 
 export type { Boss, BossStatus };