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>

server/routers/features.py

@@ -175,6 +175,7 @@ async def create_feature(project_name: str, feature: FeatureCreate):
                 description=feature.description,
                 steps=feature.steps,
                 passes=False,
+                in_progress=False,
             )
 
             session.add(db_feature)
@@ -411,6 +412,7 @@ async def create_features_bulk(project_name: str, bulk: FeatureBulkCreate):
                     description=feature_data.description,
                     steps=feature_data.steps,
                     passes=False,
+                    in_progress=False,
                 )
                 session.add(db_feature)
                 session.flush()  # Flush to get the ID immediately