Let a family carry the actors it is attributed to (#57)

[r0ny123]

Closes #57 (consider adding actors field to families).

Changes

• FamilyEntry carries actors, a list of names, in toDict()/fromDict(); families stored before this read as an empty list, so no migration. FamilyEntry.normalizeActors() strips, drops empties and duplicates, keeps the order given.
• Both storage backends accept actors in modifyFamily(); the MongoDB one sets the field on the family document.
• PUT /families/{id} accepts actors as a list of names (1 to 64 characters of letters, digits, spaces, dots, dashes, underscores; a comma separated string is accepted too); anything else is a 400 without touching the family.
• McritClient.modifyFamily(family_id, actors=[...]); an empty list clears them. The client now sends the update as JSON, since a list does not survive form encoding; the route reads req.media and takes both.
• Exports carry family_actors (family id to names, only for families that have any); imports merge them into what the target instance already knows for the remapped family. An importer without the key ignores it, an export without the key imports as before.

Verification

• tests/testFamilyActors.py (5 tests): entry round trip and legacy default; normalisation; route validation and pass-through, including the comma separated form and two rejected shapes; the client's JSON body with and without actors.
• tests/testStorage.py (both backends): set, normalised, kept through a rename, cleared, unknown family refused.
• tests/testMinHashIndex.py: an export carries the actors and an import through JSON merges them with the target's own.
• Full suite: 209 passed; ruff check, ruff format --check, ty check clean.
• Live verification on the MongoDB-backed instance follows in a comment.

[r0ny123]

Live verification on the MongoDB-backed instance (server and worker restarted on this change, through McritClient):

• modifyFamily(1, actors=[" Actor One", "Actor Two", "Actor One"]) answered "Family modified."; getFamily(1) then carried ['Actor One', 'Actor Two'], and the family document held the same.
• modifyFamily(1, actors=["<x>"]) was rejected (400) and the family stayed as it was.
• getExportData() carried family_actors: {'1': ['Actor One', 'Actor Two']}.
• modifyFamily(1, actors=[]) cleared them; getFamily(1).actors == [].