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/models/match_result.rs

@@ -1,3 +1,4 @@
+use crate::models::profile::LevelUpEvent;
 use serde::{Deserialize, Serialize};
 use uuid::Uuid;
 
@@ -77,4 +78,10 @@ pub struct MatchRewardResult {
     pub coins_awarded: i64,
     pub xp_awarded: i64,
     pub objectives_updated: Vec<String>,
+    /// Owned card IDs removed because the loan expired this match.
+    pub expired_loans: Vec<String>,
+    /// Present when this match completed the current season.
+    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>,
 }

src/models/profile.rs

@@ -30,3 +30,59 @@ impl Profile {
 pub struct CreateProfileRequest {
     pub username: Option<String>,
 }
+
+/// XP required to reach each level (cumulative total from level 1).
+/// Level 1 starts at 0 XP. Level 2 needs 500 total XP, etc.
+pub const XP_THRESHOLDS: &[i64] = &[
+    0,      // level 1
+    500,    // level 2
+    1200,   // level 3
+    2000,   // level 4
+    3000,   // level 5
+    4200,   // level 6
+    5600,   // level 7
+    7200,   // level 8
+    9000,   // level 9
+    11000,  // level 10
+];
+
+/// Compute the level for a given cumulative XP total.
+pub fn level_for_xp(total_xp: i64) -> i64 {
+    let base = XP_THRESHOLDS
+        .iter()
+        .rposition(|&t| total_xp >= t)
+        .map(|i| i as i64 + 1)
+        .unwrap_or(1);
+    // Beyond the table: every 2500 XP is another level.
+    let overflow_xp = total_xp - XP_THRESHOLDS.last().copied().unwrap_or(0);
+    if overflow_xp > 0 {
+        let table_max = XP_THRESHOLDS.len() as i64;
+        table_max + (overflow_xp / 2500)
+    } else {
+        base
+    }
+}
+
+/// Coins awarded per new level gained.
+pub fn coins_for_level(new_level: i64) -> i64 {
+    new_level * 500
+}
+
+/// Pack granted at milestone levels (5, 10, 15, 20, …).
+pub fn pack_for_level(new_level: i64) -> Option<&'static str> {
+    match new_level {
+        5  => Some("bronze_pack"),
+        10 => Some("silver_pack"),
+        15 => Some("gold_pack"),
+        20 => Some("rare_gold_pack"),
+        l if l > 20 && l % 5 == 0 => Some("gold_pack"),
+        _ => None,
+    }
+}
+
+#[derive(Debug, Clone, Serialize)]
+pub struct LevelUpEvent {
+    pub new_level: i64,
+    pub coins_granted: i64,
+    pub pack_granted: Option<String>,
+}