feat: Implement Statistics API with 8 endpoints under /api/v1/statistics/

- Add statistics.sql with 8 SQL queries for play count statistics
- Generate repository code via sqlc
- Add backend/statistics.go with business logic
- Add server/statistics_handler.go with Echo handlers
- Register protected routes under /api/v1/statistics/ with token auth
- Endpoints: games/most-played, games/least-played, games/never-played,
  games/last-played, games/oldest-played, songs/most-played,
  songs/least-played, summary

Generated by Mistral Vibe.
Co-Authored-By: Mistral Vibe <vibe@mistral.ai>

internal/db/queries/statistics.sql

@@ -0,0 +1,148 @@
+-- Most played games with their songs
+-- name: GetMostPlayedGamesWithSongs :many
+SELECT 
+    g.id as game_id,
+    g.game_name,
+    g.times_played as game_played,
+    g.last_played as game_last_played,
+    json_agg(
+        json_build_object(
+            'song_name', s.song_name,
+            'path', s.path,
+            'times_played', s.times_played,
+            'file_name', s.file_name
+        )
+    ) as songs
+FROM game g
+LEFT JOIN song s ON g.id = s.game_id
+WHERE g.deleted IS NULL
+GROUP BY g.id, g.game_name, g.times_played, g.last_played
+ORDER BY g.times_played DESC, g.game_name
+LIMIT $1;
+
+-- Least played games with their songs
+-- name: GetLeastPlayedGamesWithSongs :many
+SELECT 
+    g.id as game_id,
+    g.game_name,
+    g.times_played as game_played,
+    g.last_played as game_last_played,
+    json_agg(
+        json_build_object(
+            'song_name', s.song_name,
+            'path', s.path,
+            'times_played', s.times_played,
+            'file_name', s.file_name
+        )
+    ) as songs
+FROM game g
+LEFT JOIN song s ON g.id = s.game_id
+WHERE g.deleted IS NULL
+GROUP BY g.id, g.game_name, g.times_played, g.last_played
+ORDER BY g.times_played ASC, g.game_name
+LIMIT $1;
+
+-- Most played songs with their game info
+-- name: GetMostPlayedSongsWithGame :many
+SELECT 
+    s.game_id as game_id,
+    g.game_name,
+    s.song_name,
+    s.path,
+    s.times_played,
+    s.file_name
+FROM song s
+JOIN game g ON s.game_id = g.id
+WHERE g.deleted IS NULL
+ORDER BY s.times_played DESC, s.song_name
+LIMIT $1;
+
+-- Least played songs with their game info
+-- name: GetLeastPlayedSongsWithGame :many
+SELECT 
+    s.game_id as game_id,
+    g.game_name,
+    s.song_name,
+    s.path,
+    s.times_played,
+    s.file_name
+FROM song s
+JOIN game g ON s.game_id = g.id
+WHERE g.deleted IS NULL
+ORDER BY s.times_played ASC, s.song_name
+LIMIT $1;
+
+-- Games that have never been played (times_played = 0)
+-- name: GetNeverPlayedGames :many
+SELECT 
+    g.id as game_id,
+    g.game_name,
+    g.times_played as game_played,
+    g.added,
+    json_agg(
+        json_build_object(
+            'song_name', s.song_name,
+            'path', s.path,
+            'times_played', s.times_played
+        )
+    ) as songs
+FROM game g
+LEFT JOIN song s ON g.id = s.game_id
+WHERE g.deleted IS NULL AND g.times_played = 0
+GROUP BY g.id, g.game_name, g.times_played, g.added
+ORDER BY g.game_name;
+
+-- Last played games (most recently played)
+-- name: GetLastPlayedGames :many
+SELECT 
+    g.id as game_id,
+    g.game_name,
+    g.times_played as game_played,
+    g.last_played as game_last_played,
+    json_agg(
+        json_build_object(
+            'song_name', s.song_name,
+            'path', s.path,
+            'times_played', s.times_played
+        )
+    ) as songs
+FROM game g
+LEFT JOIN song s ON g.id = s.game_id
+WHERE g.deleted IS NULL AND g.last_played IS NOT NULL
+GROUP BY g.id, g.game_name, g.times_played, g.last_played
+ORDER BY g.last_played DESC
+LIMIT $1;
+
+-- Oldest played games (least recently played, but has been played at least once)
+-- name: GetOldestPlayedGames :many
+SELECT 
+    g.id as game_id,
+    g.game_name,
+    g.times_played as game_played,
+    g.last_played as game_last_played,
+    json_agg(
+        json_build_object(
+            'song_name', s.song_name,
+            'path', s.path,
+            'times_played', s.times_played
+        )
+    ) as songs
+FROM game g
+LEFT JOIN song s ON g.id = s.game_id
+WHERE g.deleted IS NULL AND g.last_played IS NOT NULL
+GROUP BY g.id, g.game_name, g.times_played, g.last_played
+ORDER BY g.last_played ASC
+LIMIT $1;
+
+-- Get statistics summary
+-- name: GetStatisticsSummary :one
+SELECT 
+    COUNT(*) as total_games,
+    SUM(CASE WHEN times_played > 0 THEN 1 ELSE 0 END) as played_games,
+    SUM(CASE WHEN times_played = 0 THEN 1 ELSE 0 END) as never_played_games,
+    COALESCE(SUM(times_played), 0)::bigint as total_game_plays,
+    COALESCE(AVG(times_played), 0)::float as avg_game_plays,
+    COALESCE(MAX(times_played), 0)::bigint as max_game_plays,
+    COALESCE(MIN(times_played), 0)::bigint as min_game_plays
+FROM game
+WHERE deleted IS NULL;