Add max_concurrency to Source for per-source parallelism control

ingestify/application/loader.py

@@ -253,7 +253,10 @@ def run(self, selectors, dry_run: bool = False):
                 selector=selector,
             )
 
-            with TaskExecutor(dry_run=dry_run) as task_executor:
+            with TaskExecutor(
+                dry_run=dry_run,
+                processes=ingestion_plan.source.max_concurrency,
+            ) as task_executor:
                 for ingestion_job_summary in ingestion_job.execute(
                     self.store, task_executor=task_executor
                 ):

ingestify/domain/models/source.py

@@ -7,6 +7,10 @@
 
 
 class Source(ABC):
+    # Override in subclass to limit how many tasks run in parallel.
+    # None means use the default (system concurrency).
+    max_concurrency: Optional[int] = None
+
     def __init__(self, name: str, **kwargs):
         self.name = name