perf(dav-collections): indexed UID lookups for single-object operations

Every CalDAV PUT/GET/DELETE of one .ics loaded the ENTIRE calendar —
every row including its ical_data — and filtered with .find() in Rust,
so importing N events cost O(N²) rows transferred. CardDAV did the exact
same in four places (PROPFIND of one .vcf, PUT existence check, GET,
DELETE), with three JSONB deserializations per discarded contact. The
indexed repo queries (find_event_by_ical_uid, get_contact_by_uid)
existed all along with zero callers.

Wire them end to end: new `get_event_by_ical_uid` /
`get_contact_by_uid` use-case methods (same access checks as
list_events / list_contacts, per the service-layer authz rule) exposed
through the storage ports and adapters, and the seven handler sites now
resolve one row instead of the whole collection.

https://claude.ai/code/session_01Dp3oWon5GBMVn4j3QXZdgx

src/application/ports/calendar_ports.rs

@@ -87,6 +87,14 @@ pub trait CalendarStoragePort: Send + Sync + 'static {
     ) -> Result<CalendarEventDto, DomainError>;
     async fn delete_event(&self, event_id: &str) -> Result<(), DomainError>;
     async fn get_event(&self, event_id: &str) -> Result<CalendarEventDto, DomainError>;
+    /// Indexed single-row lookup by iCalendar UID — the CalDAV
+    /// object-resource paths must use this instead of listing the whole
+    /// calendar (every row + its `ical_data`) and filtering client-side.
+    async fn find_event_by_ical_uid(
+        &self,
+        calendar_id: &str,
+        ical_uid: &str,
+    ) -> Result<Option<CalendarEventDto>, DomainError>;
     async fn list_events_by_calendar(
         &self,
         calendar_id: &str,
@@ -180,6 +188,15 @@ pub trait CalendarUseCase: Send + Sync + 'static {
         event_id: &str,
         user_id: Uuid,
     ) -> Result<CalendarEventDto, DomainError>;
+    /// Resolve one event by its iCalendar UID (the identifier CalDAV
+    /// object resources are addressed by). `Ok(None)` when no event with
+    /// that UID exists in the calendar.
+    async fn get_event_by_ical_uid(
+        &self,
+        calendar_id: &str,
+        ical_uid: &str,
+        user_id: Uuid,
+    ) -> Result<Option<CalendarEventDto>, DomainError>;
     async fn list_events(
         &self,
         calendar_id: &str,