Phase 20: achievement system

18 data-driven achievements (achievements.json) across 8 trigger categories:
matches_played, matches_won, goals_scored, packs_opened, sbcs_completed,
cards_owned, level, objectives_completed, drafts_completed. Rarities span
common → epic. Coin rewards range from 500 (first_match) to 6000 (win_50).

check_and_unlock() queries the relevant metric from existing tables, skips
already-earned achievements via INSERT OR IGNORE, grants coin rewards, and
fires a persistent notification per unlock. Trigger values are cached per
call to avoid redundant DB round-trips for same-trigger achievements.

Checks run automatically after every match result (all triggers), every
pack open (packs_opened), and every successful SBC submission (sbcs_completed).

GET /achievements returns all definitions annotated with unlocked/unlocked_at,
plus earned and total counts. POST /matches/result response gains an
achievements_unlocked array (empty when nothing new unlocked).

AppState gains achievement_defs (Arc<Vec<AchievementDefinition>>) loaded
from data/achievements/**/*.json at startup — same pattern as obj_defs.

5 new tests: list endpoint, first_match unlock, first_win unlock, no-dup
guard, coin reward verification. Core now at 82 tests.

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

src/models/match_result.rs

@@ -1,4 +1,4 @@
-use crate::models::profile::LevelUpEvent;
+use crate::models::{achievement::AchievementDefinition, profile::LevelUpEvent};
 use serde::{Deserialize, Serialize};
 use uuid::Uuid;
 
@@ -84,4 +84,6 @@ pub struct MatchRewardResult {
     pub season_end: Option<crate::models::season::SeasonEndSummary>,
     /// Non-empty when the player levelled up one or more times from this match's XP.
     pub level_ups: Vec<LevelUpEvent>,
+    /// Achievements unlocked as a result of this match.
+    pub achievements_unlocked: Vec<AchievementDefinition>,
 }