feat(backend): migration mekanizması, indeksler ve ortak model yardımcıları

- db/migrations.rs: schema_migrations ile sürümlü migration (v1: koleksiyonlar)
- db/indexes.rs: DATA_MODEL indeksleri + senkronizasyon indeksi, açılışta otomatik
- models/common.rs: UUID v7, ortak alanlar, hane kapsamlı filtre
- Birim testleri (4)

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

backend/src/db/indexes.rs

@@ -0,0 +1,116 @@
+//! İndeksler (DATA_MODEL.md §4). Açılışta her seferinde çağrılır;
+//! MongoDB zaten var olan aynı indeksi yeniden oluşturmaz.
+
+use mongodb::{
+    Database, IndexModel,
+    bson::{Document, doc},
+    error::Result,
+    options::IndexOptions,
+};
+
+use super::col;
+
+pub async fn ensure(db: &Database) -> Result<()> {
+    for (collection, indexes) in definitions() {
+        db.collection::<Document>(collection)
+            .create_indexes(indexes)
+            .await?;
+    }
+    tracing::info!("İndeksler hazır");
+    Ok(())
+}
+
+fn idx(keys: Document) -> IndexModel {
+    IndexModel::builder().keys(keys).build()
+}
+
+fn idx_opts(keys: Document, options: IndexOptions) -> IndexModel {
+    IndexModel::builder().keys(keys).options(options).build()
+}
+
+fn unique() -> IndexOptions {
+    IndexOptions::builder().unique(true).build()
+}
+
+fn definitions() -> Vec<(&'static str, Vec<IndexModel>)> {
+    let hp = || idx(doc! { "household_id": 1, "period_id": 1 });
+
+    let mut defs = vec![
+        (col::USERS, vec![idx_opts(doc! { "email": 1 }, unique())]),
+        (col::INVITES, vec![idx_opts(doc! { "code": 1 }, unique())]),
+        (
+            col::PERIODS,
+            vec![
+                idx(doc! { "household_id": 1, "start_date": 1 }),
+                // Hanede en fazla bir açık dönem
+                idx_opts(
+                    doc! { "household_id": 1 },
+                    IndexOptions::builder()
+                        .name("one_open_period_per_household".to_string())
+                        .unique(true)
+                        .partial_filter_expression(doc! { "status": "open" })
+                        .build(),
+                ),
+            ],
+        ),
+        (
+            col::CATEGORIES,
+            vec![idx(doc! { "household_id": 1, "sort_order": 1 })],
+        ),
+        (
+            col::PAYMENT_METHODS,
+            vec![idx(doc! { "household_id": 1, "sort_order": 1 })],
+        ),
+        (col::PLAN_ITEMS, vec![hp()]),
+        (col::BUDGETS, vec![hp()]),
+        (col::NOTES, vec![hp()]),
+        (
+            col::ENTRIES,
+            vec![
+                idx(doc! { "household_id": 1, "period_id": 1, "date": 1 }),
+                idx(doc! { "household_id": 1, "date": 1 }),
+            ],
+        ),
+        (
+            col::CARRYOVERS,
+            vec![idx(doc! { "household_id": 1, "to_period_id": 1 })],
+        ),
+        (
+            col::ASSET_TRANSACTIONS,
+            vec![idx(doc! { "household_id": 1, "asset_id": 1, "date": 1 })],
+        ),
+        (
+            col::EXCHANGE_RATES,
+            vec![idx(doc! { "code": 1, "household_id": 1, "rate_date": -1 })],
+        ),
+    ];
+
+    // Senkronizasyon (Faz 11): "şu tarihten sonra değişenler" sorgusu.
+    for &name in col::HOUSEHOLD_SCOPED {
+        let sync = idx(doc! { "household_id": 1, "updated_at": 1 });
+        match defs.iter_mut().find(|(c, _)| *c == name) {
+            Some((_, list)) => list.push(sync),
+            None => defs.push((name, vec![sync])),
+        }
+    }
+
+    defs
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn every_household_collection_has_sync_index() {
+        let defs = definitions();
+        for &name in col::HOUSEHOLD_SCOPED {
+            let (_, list) = defs.iter().find(|(c, _)| *c == name).unwrap();
+            assert!(
+                list.iter()
+                    .any(|i| i.keys == doc! { "household_id": 1, "updated_at": 1 }),
+                "{name} koleksiyonunda senkronizasyon indeksi yok"
+            );
+        }
+    }
+}