perf(db): enable WAL mode, add tuning pragmas and missing indexes

- Enable WAL journal mode for concurrent reads during writes
- Set synchronous=NORMAL, cache_size=8MB, temp_store=MEMORY, busy_timeout=5s
- Add indexes on brews.grinder_id, brews.brewer_id, brews.filter_paper_id
  to speed up the 6-table brew list JOIN
- Gitignore WAL sidecar files (*.db-shm, *.db-wal)

.gitignore

@@ -2,6 +2,8 @@ target/
 result*
 *.db
 *.db-journal
+*.db-shm
+*.db-wal
 TODO.md
 backup.json
 *.env

migrations/0005_brew_gear_indexes.sql

@@ -0,0 +1,7 @@
+-- Add missing indexes on brew foreign keys to gear table.
+-- The brew list query joins gear 3 times (grinder, brewer, filter paper);
+-- these indexes avoid full table scans on the gear side of each join.
+
+CREATE INDEX idx_brews_grinder_id ON brews(grinder_id);
+CREATE INDEX idx_brews_brewer_id ON brews(brewer_id);
+CREATE INDEX idx_brews_filter_paper_id ON brews(filter_paper_id);

src/infrastructure/database.rs

@@ -33,6 +33,31 @@ impl Database {
             .await
             .context("failed to enable foreign keys for sqlite")?;
 
+        sqlx::query("PRAGMA journal_mode = WAL;")
+            .execute(&pool)
+            .await
+            .context("failed to enable WAL journal mode for sqlite")?;
+
+        sqlx::query("PRAGMA synchronous = NORMAL;")
+            .execute(&pool)
+            .await
+            .context("failed to set synchronous mode for sqlite")?;
+
+        sqlx::query("PRAGMA cache_size = -8000;")
+            .execute(&pool)
+            .await
+            .context("failed to set cache size for sqlite")?;
+
+        sqlx::query("PRAGMA temp_store = MEMORY;")
+            .execute(&pool)
+            .await
+            .context("failed to set temp_store for sqlite")?;
+
+        sqlx::query("PRAGMA busy_timeout = 5000;")
+            .execute(&pool)
+            .await
+            .context("failed to set busy_timeout for sqlite")?;
+
         let db = Self { pool };
         db.migrate().await?;
         Ok(db)