Reliable indexing of private / made-public parts (fixes #158, #159)

[cl117]

• Private parts are indexed on upload and searchable immediately via the normal ES path — no separate private-Virtuoso routing needed.

• Removed / made-private parts leave the index at once; made-public parts get a sensible (floor) rank instead of dominating results.

• Multi-typed parts index correctly on single-part refresh.

• Empty search no longer crashes when no graph is supplied.

• A logged-in user's private graph is correctly included in search, so private parts are searchable by their owner through the normal Elasticsearch path.