fix: preserve all-time stats, achievements, and boss first-kill across prestige (#47)

Resolves #37, resolves #38, and resolves #39 — three related bugs where prestige incorrectly reset data that should survive all prestige resets.

## Changes

### fix: preserve lifetime player stats across prestige (#37)
After prestige, `GameState.player.lifetime*` fields were stale — they reflected values from *before* the current run. The Prisma Player record was incremented correctly, but the GameState JSON saved to the DB had old values, so the UI showed wrong all-time totals on reload.

`buildPostPrestigeState` now computes the run-stat contributions (bosses defeated, quests completed, adventurers recruited, achievements unlocked, gold earned, clicks) and folds them into the fresh player object before writing the prestige state.

### fix: preserve achievements across prestige (#38)
`buildPostPrestigeState` was reconstructing achievements from `defaultAchievements` (via `initialGameState`), resetting all unlocked achievements on every prestige. Achievements are now carried forward from `currentState.achievements` instead.

### fix: preserve boss first-kill state across prestige (#39)
Added `bountyRunestonesClaimed?: boolean` to the `Boss` type. The boss challenge route now:
- Only awards the first-kill bounty runestones if `bountyRunestonesClaimed !== true`
- Sets `bountyRunestonesClaimed = true` on first defeat

`buildPostPrestigeState` maps the fresh boss list and carries the `bountyRunestonesClaimed` flag forward from the current state, so the bounty is never re-awarded in subsequent prestige runs. The boss panel badge is also hidden for bosses whose bounty is already claimed.

## Test Coverage
All three fixes include new tests covering the new behaviours. API coverage remains at 100%.

✨ This PR was created with help from Hikari~ 🌸

Reviewed-on: #47
Co-authored-by: Hikari <hikari@nhcarrigan.com>
Co-committed-by: Hikari <hikari@nhcarrigan.com>

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 };