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/embed.rs

@@ -19,10 +19,13 @@ pub struct EmbedCommandResult {
 }
 
 /// Run the embed command.
+///
+/// `progress_callback` reports `(processed, total)` as documents are embedded.
 pub async fn run_embed(
     config: &Config,
     full: bool,
     retry_failed: bool,
+    progress_callback: Option<Box<dyn Fn(usize, usize)>>,
 ) -> Result<EmbedCommandResult> {
     let db_path = get_db_path(config.storage.db_path.as_deref());
     let conn = create_connection(&db_path)?;
@@ -58,7 +61,7 @@ pub async fn run_embed(
     }
 
     let model_name = &config.embedding.model;
-    let result = embed_documents(&conn, &client, model_name, None).await?;
+    let result = embed_documents(&conn, &client, model_name, progress_callback).await?;
 
     Ok(EmbedCommandResult {
         embedded: result.embedded,