Cardano Updates

git's three-way merge of preprod←main reported a clean merge of
prisma/schema.prisma and src/server/api/trpc.ts but silently dropped
main's additions — both files had only end-of-file additions on main,
which the auto-merge resolved by taking preprod's tail without pulling
in main's new symbols. The Vercel build then failed on three downstream
references.

prisma/schema.prisma
- Add model AuditLog (referenced by src/lib/observability/audit.ts;
  migration 20260510160404_audit_log_and_indexes already in the tree)
- Make User.nostrKey String? (matches migration
  20260510170000_make_user_nostrkey_optional)

src/server/api/trpc.ts
- Re-export TRPCContext and AuthCtx (used by src/server/api/auth.ts
  added in main's audit-log PR)

Drop the Nostr chat system on preprod to match main
- Remove src/components/pages/wallet/chat and src/pages/wallets/[wallet]/chat
- Drop @jinglescode/nostr-chat-plugin imports from _app.tsx + layout.tsx
- Remove the Chat menu entry from the wallet sidebar
- userRouter.createUser: nostrKey becomes optional (matches the now-
  nullable column) and is only written when supplied
- User profile page: scope nostrKey to a non-null local inside the
  existing `user.nostrKey &&` guard so it still renders for legacy
  users without tripping the nullable narrowing

The repo's nostr-chat-plugin dep was already removed in the prior
merge commit; this commit removes the last call sites and brings the
user-row contract in line with the schema.

Co-Authored-By: Claude Opus 4.7 (1M context) <[email protected]>

The tests started to fail due to usage of version data codec which
doesn't satisfy round robin property on invalid version data in the
previous commit.

We used to need to call `cborTermVersionDataCodec` to get
`VersionDataCodec` from `CodecCBORTerm`.

The `VersionDataCodec` and `cborTermVersionDataCodec` is moved to
`ouroboros-network:api` library (`Ouroboros.network.CodecCBORTerm`
module).

`cardano-diffusion` provides both `nodeToNodeVersionDataCodec` and
`nodeToClientVersionDataCodec`.

This required a refactorisation in tests to get rid of some newtype
wrappers, however the semantics of all the tests is preserved.

Let's hard code `PerasSupported`, which allows to query nodes if they
support Peras without breaking nodes which don't support it.

Exposed `nodeTo{Node,Client}VersionDataCodec` instead.

The instantiation of `ChainSync` is polymorphic enough to support both
protocols.

mkdocs .md files weren't being generated even when .lagda.md files changed.