feat(sync): Wire progress callbacks through sync pipeline stages

The sync command's stage spinners now show real-time aggregate progress
for each pipeline phase instead of static "syncing..." messages.

- Add `progress_callback` parameter to `run_embed` and
  `run_generate_docs` so callers can receive `(processed, total)` updates
- Add `stage_bar` parameter to `run_ingest` for aggregate progress
  across concurrently-ingested projects using shared AtomicUsize counters
- Update `stage_spinner` to use `{prefix}` for the `[N/M]` label,
  allowing `{msg}` to be updated independently with progress details
- Thread `ProgressBar` clones into each concurrent project task so
  per-entity progress (fetch, discussions, events) is reflected on the
  aggregate spinner
- Pass `None` for progress callbacks at standalone CLI entry points
  (handle_ingest, handle_generate_docs, handle_embed) to preserve
  existing behavior when commands are run outside of sync

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

src/cli/commands/generate_docs.rs

@@ -28,10 +28,13 @@ pub struct GenerateDocsResult {
 ///
 /// Default mode: process only existing dirty_sources entries.
 /// Full mode: seed dirty_sources with ALL entities, then drain.
+///
+/// `progress_callback` reports `(processed, estimated_total)` as documents are generated.
 pub fn run_generate_docs(
     config: &Config,
     full: bool,
     project_filter: Option<&str>,
+    progress_callback: Option<Box<dyn Fn(usize, usize)>>,
 ) -> Result<GenerateDocsResult> {
     let db_path = get_db_path(config.storage.db_path.as_deref());
     let conn = create_connection(&db_path)?;
@@ -46,7 +49,8 @@ pub fn run_generate_docs(
         result.seeded += seed_dirty(&conn, SourceType::Discussion, project_filter)?;
     }
 
-    let regen = regenerate_dirty_documents(&conn)?;
+    let regen =
+        regenerate_dirty_documents(&conn, progress_callback.as_ref().map(|cb| cb.as_ref()))?;
     result.regenerated = regen.regenerated;
     result.unchanged = regen.unchanged;
     result.errored = regen.errored;