style: fmt + clippy cleanup after Phase B

cargo fmt regroups, plus three Phase-B clippy fixes:
- F-P-004: #[allow(clippy::type_complexity)] on the invoke_ast_cache Mutex.
- F-P-008: hoist `futures::stream::{self, TryStreamExt}` to the top-of-
  file imports to satisfy clippy::items_after_statements.
- F-P-005: rename `_legacy_offset` to `legacy_offset` + #[allow(dead_code)]
  to satisfy clippy's "field is pub but `_`-prefixed" check.

No behavior change.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

crates/manager-core/src/trigger_repo.rs

@@ -5,6 +5,7 @@
 
 use async_trait::async_trait;
 use chrono::{DateTime, Utc};
+use futures::stream::{self, TryStreamExt};
 use picloud_shared::{
     AdminUserId, AppId, DocsEventOp, FilesEventOp, KvEventOp, ScriptId, TriggerId,
 };
@@ -984,7 +985,6 @@ impl TriggerRepo for PostgresTriggerRepo {
         // sum(per-row-latency). Still N+1 queries against the details
         // tables — collapsing to a single per-kind LEFT JOIN is a
         // larger SQL refactor tracked as v1.2.
-        use futures::stream::{self, TryStreamExt};
         let pool = self.pool.clone();
         let out = stream::iter(parents.into_iter().map(Ok))
             .map_ok(|p| {