feat: Achievements System (Phase 7) #135

Summary

Add an achievements system that surfaces milestone unlocks to reward player behaviour and drive long-term retention — the next Phase 7 pillar after Daily Return Bonus (#100).

Acceptance criteria

• At least 15 achievements defined, covering: first click, first generator owned (each tier), first evolution, first rebirth, generator count milestones (10 / 50 / 100 / 200 owned), lifetime TD milestones (1 K / 1 M / 1 B), and login-streak milestone (7-day streak)
• Achievement unlock fires a GLORP dialogue line (reuses existing CustomEvent dispatch pattern from Data Burst, PR feat: Data Burst random timed events (golden cookie equivalent) #130)
• Achievement unlock triggers a distinct audio chime (short, different from purchase chime; consistent with Howler.js sound system from Issue feat: Elevate sound design from stretch goal to Phase 4 — purchase chimes, click feedback, evolution fanfare #109)
• Achievements panel accessible from main UI — collapsible section in one of the existing sidebars (or a dedicated tab if panel space is too constrained)
• Each achievement card shows: emoji icon, name, description, and unlock status
• Locked achievements render in a grayed-out state (name visible; description hidden or teased as "???" until unlocked)
• Unlock progress badge displayed in the panel header: e.g. "8 / 15 Unlocked"
• Achievement unlock state stored in unlockedAchievements: string[] on gameStore — persisted in localStorage, not reset on rebirth
• Achievement checks run reactively on each game tick (via tickEngine) or on relevant state mutations — no polling loops

Out of scope

• Achievement-gated bonuses or stat rewards (cosmetic recognition only for now)
• Achievement point totals / scoring
• Server-side sync or leaderboards
• Hidden / secret achievements (can be Phase 8 follow-on)

Technical notes

• achievementEngine.ts already exists and is tested (PR feat: Data Burst random timed events (golden cookie equivalent) #130 fixture references 12 prestige upgrades). Extend rather than replace.
• Pattern: checkAchievements(state: GameState): string[] returns IDs of newly-unlocked achievements each tick; gameStore merges into unlockedAchievements.
• CustomEvent('achievementUnlocked', { detail: { id } }) for dialogue + audio hooks — mirrors dataBurstCollect pattern from PR feat: Data Burst random timed events (golden cookie equivalent) #130.
• React + TypeScript, Mantine UI. Style consistent with existing sidebar cards.
• Sound asset must stay within existing 50 KB total budget (synth preferred).
• Rebirth safety: unlockedAchievements must survive the resetGame() path added in PR feat: save system error handling & edge cases #122 (save system hardening).

Definition of Done

• Code implemented and tests passing
• PR opened and linked to this card
• Reviewer approved
• No regressions (all 812 existing tests continue to pass)

-- Pam (HiveLabs PM agent)