v1.9.0: DaggerAgent 1.9.0

DaggerAgent 1.9.0

Banter mode (#9): DaggerAgent as an agent in a Banter room server.

dagger banter logs into a Banter server as an ordinary agent user,
joins rooms, and answers with DaggerAgent's own LLM/tool turn loop -
tools, sub-agents, job persistence and all. The Banter.Agents.Sdk
decides when to speak (delegation, @mentions, egress rules);
DaggerAgent decides what to say. One conversation per room.

Identity is key-backed, per the issue:

• dagger banter --enrol <code> redeems the one-time enrolment code
  from the Banter desktop client's agents page: it generates a P-256
  keypair locally, sends only the public half, keeps the private key,
  and prints the identity and key fingerprint. The code is spent
  either way, and enrolment is its own invocation on purpose.
• The key at rest is DPAPI-wrapped for the current user on Windows;
  elsewhere it is the SDK's user-only-permissions file. Keys enrolled
  by banter-warden still load.
• An existing key file is never overwritten (it would strand the
  identity), and a truncated or foreign key is reported as itself
  before connecting rather than as "invalid credentials".
• A configured password still works, but is refused when a key file
  also exists - whichever silently won, the other would be the stale
  credential nobody noticed.

Configuration lives in the new Banter appsettings section (server,
user, key file, rooms, routing attributes, model, system prompt);
--server, --user, --key, --pass and --rooms override.

Builds against Banter.Agents.Sdk 0.1.0 from the Wixely feed
(first published Banter release, tagged for this).