fix(ingestion): Move counter increments after transaction commit

Ingestion counters (discussions_upserted, notes_upserted,
discussions_fetched, diffnotes_count) were incremented before
tx.commit(), meaning a failed commit would report inflated
metrics. Counters now increment only after successful commit
so reported numbers accurately reflect persisted state.

Also simplifies the stale-removal guard in issue discussions:
the received_first_response flag was unnecessary since an empty
seen_discussion_ids list is safe to pass to remove_stale -- if
there were no discussions, stale removal correctly sweeps all
previously-stored discussions. The two separate code paths
(empty vs populated) are collapsed into a single branch.

Derives Default on IngestResult to eliminate verbose zero-init.

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

src/cli/commands/ingest.rs

@@ -17,6 +17,7 @@ use crate::ingestion::{
 };
 
 /// Result of ingest command for display.
+#[derive(Default)]
 pub struct IngestResult {
     pub resource_type: String,
     pub projects_synced: usize,
@@ -130,24 +131,7 @@ pub async fn run_ingest(
 
     let mut total = IngestResult {
         resource_type: resource_type.to_string(),
-        projects_synced: 0,
-        // Issue fields
-        issues_fetched: 0,
-        issues_upserted: 0,
-        issues_synced_discussions: 0,
-        issues_skipped_discussion_sync: 0,
-        // MR fields
-        mrs_fetched: 0,
-        mrs_upserted: 0,
-        mrs_synced_discussions: 0,
-        mrs_skipped_discussion_sync: 0,
-        assignees_linked: 0,
-        reviewers_linked: 0,
-        diffnotes_count: 0,
-        // Shared fields
-        labels_created: 0,
-        discussions_fetched: 0,
-        notes_upserted: 0,
+        ..Default::default()
     };
 
     let type_label = if resource_type == "issues" {