fix: add explicit in_progress=False to all feature creation paths

Complete the defense-in-depth approach from PR #53 by adding explicit
in_progress=False to all remaining feature creation locations. This
ensures consistency with the MCP server pattern and prevents potential
NULL values in the in_progress field.

Changes:
- server/routers/features.py: Add in_progress=False to create_feature()
  and create_features_bulk() endpoints
- server/services/expand_chat_session.py: Add in_progress=False to
  _create_features_bulk() in the expand chat session
- api/migration.py: Add in_progress field handling in JSON migration,
  reading from source data with False as default

This follows up on PR #53 which added nullable=False constraints and
fixed existing NULL values, but only updated the MCP server creation
paths. Now all 6 feature creation locations explicitly set both
passes=False and in_progress=False.

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

api/migration.py

@@ -82,6 +82,7 @@ def migrate_json_to_sqlite(
                 description=feature_dict.get("description", ""),
                 steps=feature_dict.get("steps", []),
                 passes=feature_dict.get("passes", False),
+                in_progress=feature_dict.get("in_progress", False),
             )
             session.add(feature)
             imported_count += 1