fix(ingestion): pass ShutdownSignal into issue and MR pagination loops

The orchestrator already accepted a ShutdownSignal but only checked it
between phases (after all issues fetched, before discussions). The inner
loops in ingest_issues() and ingest_merge_requests() consumed entire
paginated streams without checking for cancellation.

On a large initial sync (thousands of issues/MRs), Ctrl+C could be
unresponsive for minutes while the current entity type finished draining.

Now both functions accept &ShutdownSignal and check is_cancelled() at
the top of each iteration, breaking out promptly and committing the
cursor for whatever was already processed.

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

src/ingestion/merge_requests.rs

@@ -6,6 +6,7 @@ use tracing::{debug, info, warn};
 use crate::Config;
 use crate::core::error::{LoreError, Result};
 use crate::core::payloads::{StorePayloadOptions, store_payload};
+use crate::core::shutdown::ShutdownSignal;
 use crate::core::time::now_ms;
 use crate::documents::SourceType;
 use crate::gitlab::GitLabClient;
@@ -42,6 +43,7 @@ pub async fn ingest_merge_requests(
     project_id: i64,
     gitlab_project_id: i64,
     full_sync: bool,
+    signal: &ShutdownSignal,
 ) -> Result<IngestMergeRequestsResult> {
     let mut result = IngestMergeRequestsResult::default();
 
@@ -58,6 +60,10 @@ pub async fn ingest_merge_requests(
     let per_page = 100u32;
 
     loop {
+        if signal.is_cancelled() {
+            info!("MR ingestion interrupted by shutdown signal");
+            break;
+        }
         let page_result = client
             .fetch_merge_requests_page(
                 gitlab_project_id,