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/documents/regenerator.rs

@@ -1,6 +1,6 @@
 use rusqlite::Connection;
 use rusqlite::OptionalExtension;
-use tracing::{debug, warn};
+use tracing::{debug, instrument, warn};
 
 use crate::core::error::Result;
 use crate::documents::{
@@ -21,6 +21,7 @@ pub struct RegenerateResult {
 ///
 /// Uses per-item error handling (fail-soft) and drains the queue completely
 /// via a bounded batch loop. Each dirty item is processed independently.
+#[instrument(skip(conn), fields(items_processed, items_skipped, errors))]
 pub fn regenerate_dirty_documents(conn: &Connection) -> Result<RegenerateResult> {
     let mut result = RegenerateResult::default();
 
@@ -61,6 +62,10 @@ pub fn regenerate_dirty_documents(conn: &Connection) -> Result<RegenerateResult>
         "Document regeneration complete"
     );
 
+    tracing::Span::current().record("items_processed", result.regenerated);
+    tracing::Span::current().record("items_skipped", result.unchanged);
+    tracing::Span::current().record("errors", result.errored);
+
     Ok(result)
 }
 
@@ -282,6 +287,7 @@ mod tests {
                 updated_at INTEGER NOT NULL,
                 last_seen_at INTEGER NOT NULL,
                 discussions_synced_for_updated_at INTEGER,
+                resource_events_synced_for_updated_at INTEGER,
                 web_url TEXT,
                 raw_payload_id INTEGER
             );