feat: add account and space inboxes

[pcarranzav]

Implements inboxes as described in #133.

Inboxes can be created for accounts or for spaces.
Some simple demo interfaces are provided for both in the events app: a space chat, and a way to send messages to account inboxes for the test accounts.

A complete interface is implemented in useHypergraphApp, but a simpler API is available with useSpaceInbox and useAccountInbox.

Future improvements can be made in other PRs:

• Iterate on the interfaces, maybe add an ensureAccountInbox like we have for space inboxes?
• Iterate on how we store the inboxes and messages, currently this is part of the SpaceStorageEntry so we might re-render too many things when a message is received. It might be better to store space inboxes in their own storage entry separate from spaces?
• Add the ability to create inboxes that accept specific schemas or arbitrary knowledge

[Copilot]

Copilot reviewed 45 out of 47 changed files in this pull request and generated 1 comment.

Files not reviewed (2)

• apps/server/prisma/migrations/20250306204530_add_inboxes/migration.sql: Language not supported
• apps/server/prisma/schema.prisma: Language not supported

Comments suppressed due to low confidence (1)

apps/events/src/routes/space/$spaceId.tsx:110

• The 'plaintext' property is referenced when displaying messages, but the corresponding message objects only include ciphertext. Please review how message decryption or the property naming should be handled.

<div>{msg.plaintext}</div>

[nikgraf]

yay, let's ship it 👏