Add document I/O to workflows and surface run artifacts

Let workflow runs consume and produce documents end to end: bridge uploaded
attachments into run-scoped artifacts so nodes receive the input documents
(with a per-run cap and server-computed size/sha256, and the run row pre-created
so produced artifacts are authorized during the run); emit the run id to the
client and add a builder panel that lists, previews, and downloads a run's
artifacts; and allow attaching documents to a Preview run via the existing
upload flow.

Also fixes issues a compliance workflow surfaced: attachment ownership now keys
on the raw identity instead of a sanitized one (the sanitized form could not be
read back and could collide across users); workflow code nodes read prior state
from a state.json data file instead of templating it into the program, so
untrusted document content can never be interpolated into executed code;
structured node output wrapped in code fences is recovered; and the live
speech-to-text ownership check compares the raw identity.

tests/agents/test_workflow_agent_pg_write.py

@@ -1,4 +1,4 @@
-"""Tests for the Postgres dual-write path inside WorkflowAgent._save_workflow_run.
+"""Tests for the Postgres write path inside WorkflowAgent._finalize_workflow_run.
 
 Specifically verifies the inner ``_pg_write`` closure that:
 1. Calls WorkflowsRepository.get_by_legacy_id() to resolve the Mongo workflow id.
@@ -64,7 +64,7 @@ def _stub_mongo(agent, insert_id=None):
 
 
 # ---------------------------------------------------------------------------
-# _save_workflow_run — PG dual-write logic
+# _finalize_workflow_run — PG write logic
 # ---------------------------------------------------------------------------