feat(sync): Instrument pipeline with tracing spans, run_id correlation, and metrics

Add end-to-end observability to the sync and ingest pipelines:

Sync command:
- Generate UUID-based run_id for each sync invocation, propagated through
  all child spans for log correlation across stages
- Accept MetricsLayer reference to extract hierarchical StageTiming data
  after pipeline completion for robot-mode performance output
- Record sync runs in DB via SyncRunRecorder (start/succeed/fail lifecycle)
- Wrap entire sync execution in a root tracing span with run_id field

Ingest command:
- Wrap run_ingest in an instrumented root span with run_id and resource_type
- Add project path prefix to discussion progress bars for multi-project clarity
- Reset resource_events_synced_for_updated_at on --full re-sync

Sync status:
- Expand from single last_run to configurable recent runs list (default 10)
- Parse and expose StageTiming metrics from stored metrics_json
- Add run_id, total_items_processed, total_errors to SyncRunInfo
- Add mr_count to DataSummary for complete entity coverage

Orchestrator:
- Add #[instrument] with structured fields to issue and MR ingestion functions
- Record items_processed, items_skipped, errors on span close for MetricsLayer
- Emit granular progress events (IssuesFetchStarted, IssuesFetchComplete)
- Pass project_id through to drain_resource_events for scoped job claiming

Document regenerator and embedding pipeline:
- Add #[instrument] spans with items_processed, items_skipped, errors fields
- Record final counts on span close for metrics extraction

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

src/embedding/pipeline.rs

@@ -4,7 +4,7 @@ use std::collections::HashSet;
 
 use rusqlite::Connection;
 use sha2::{Digest, Sha256};
-use tracing::{info, warn};
+use tracing::{info, instrument, warn};
 
 use crate::core::error::Result;
 use crate::embedding::change_detector::{count_pending_documents, find_pending_documents};
@@ -37,6 +37,7 @@ struct ChunkWork {
 ///
 /// Processes batches of BATCH_SIZE texts per Ollama API call.
 /// Uses keyset pagination over documents (DB_PAGE_SIZE per page).
+#[instrument(skip(conn, client, progress_callback), fields(%model_name, items_processed, items_skipped, errors))]
 pub async fn embed_documents(
     conn: &Connection,
     client: &OllamaClient,
@@ -87,7 +88,7 @@ pub async fn embed_documents(
             // Overflow guard: skip documents that produce too many chunks.
             // Must run BEFORE clear_document_embeddings so existing embeddings
             // are preserved when we skip.
-            if total_chunks as i64 >= CHUNK_ROWID_MULTIPLIER {
+            if total_chunks as i64 > CHUNK_ROWID_MULTIPLIER {
                 warn!(
                     doc_id = doc.document_id,
                     chunk_count = total_chunks,
@@ -295,6 +296,10 @@ pub async fn embed_documents(
         "Embedding pipeline complete"
     );
 
+    tracing::Span::current().record("items_processed", result.embedded);
+    tracing::Span::current().record("items_skipped", result.skipped);
+    tracing::Span::current().record("errors", result.failed);
+
     Ok(result)
 }