Phase 17: profile level-up system

XP thresholds (500→1200→2000→…→11000→+2500/level) drive automatic level
increases. add_xp_with_levelup() replaces bare add_xp() in match
processing: for each level gained it grants level×500 coins and milestone
packs (bronze@5, silver@10, gold@15, rare_gold@20, gold every 5 after).

GET /profile now returns computed level (recalculated from XP so it
stays consistent), xp_to_next_level, and xp_for_next_level so the
dashboard can render a progress bar without a second call.

POST /matches/result response gains level_ups array (empty when no
level-up occurred) with new_level, coins_granted, pack_granted per event.

Four new tests: profile level fields, level_for_xp boundary checks,
level-up event in match result, milestone pack unit test.

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

src/routes/profile.rs

@@ -1,9 +1,34 @@
 use crate::{
-    app::AppState, error::AppResult, models::profile::Profile, services::profile as profile_svc,
+    app::AppState,
+    error::AppResult,
+    models::profile::{level_for_xp, XP_THRESHOLDS},
+    services::profile as profile_svc,
 };
 use axum::{extract::State, Json};
+use serde_json::{json, Value};
 
-pub async fn get_profile(State(state): State<AppState>) -> AppResult<Json<Profile>> {
+pub async fn get_profile(State(state): State<AppState>) -> AppResult<Json<Value>> {
     let profile = profile_svc::get_active_profile(&state.pool).await?;
-    Ok(Json(profile))
+    let computed_level = level_for_xp(profile.xp);
+
+    let next_level = computed_level + 1;
+    let xp_for_next = if next_level as usize <= XP_THRESHOLDS.len() {
+        XP_THRESHOLDS[next_level as usize - 1]
+    } else {
+        let overflow_base = XP_THRESHOLDS.last().copied().unwrap_or(0);
+        let levels_past = next_level - XP_THRESHOLDS.len() as i64;
+        overflow_base + levels_past * 2500
+    };
+    let xp_to_next = (xp_for_next - profile.xp).max(0);
+
+    Ok(Json(json!({
+        "id": profile.id,
+        "username": profile.username,
+        "level": computed_level,
+        "xp": profile.xp,
+        "xp_to_next_level": xp_to_next,
+        "xp_for_next_level": xp_for_next,
+        "created_at": profile.created_at,
+        "updated_at": profile.updated_at,
+    })))
 }