Show remote clanker avatar in TUI during inter-agent communication

[hai-pilgrim]

Context

When one clanker instance communicates with another (e.g. via subagent delegation, MCP, or collaboration modes), the TUI currently shows only the local clanker's avatar. There is no visual representation of the remote agent's identity.

For clanker-code's identity-first vision, when Pilgrim talks to HAI, the TUI should show both avatars — Pilgrim on one side, HAI on the other — making the conversation feel like a dialogue between two embodied agents, not a monologue with tool calls.

What is needed

1. Remote avatar discovery. When a clanker-to-clanker session is established (via collaboration mode, subagent spawning, or MCP), the remote agent's character manifest (name, avatar) should be discoverable. This could be via:

   • Protocol exchange (the remote agent advertises its identity on connection)
   • Shared character registry
   • Manual configuration

2. Dual-avatar TUI layout. The TUI should support displaying two avatars:

   • Local avatar (left/top) — the current user's clanker persona
   • Remote avatar (right/bottom) — the peer clanker's persona
   • The remote avatar animates (talking, idle) based on whose turn it is in the conversation

3. Graceful fallback. If the remote agent's avatar is unavailable (e.g. upstream codex agent without character manifest), show a generic placeholder or just the name.

4. Multi-peer support. In collaboration modes with more than two agents, the TUI should handle displaying multiple peer identities (at minimum their names, ideally small avatars).

Depends on

• Disentangle clanker avatar from the pets subsystem #42 (avatar disentanglement from pets) — avatar must be a standalone concept to render multiples
• Persona-first TUI: name and identity as the primary TUI anchor #41 (persona-first TUI) — identity display infrastructure
• Read AGENT_PERSONA envvar as first-class identity input and select histories by persona name #40 (AGENT_PERSONA) — identity resolution for the local side

Relationship to existing issues

• Room is a manifest field with no runtime: half-block room composition unimplemented #37 (room composition) — the "room" concept could naturally frame multi-agent avatar layouts
• Voice workstream not started: clanker-voice plugin, Ears speech input, say output, playback animation #35 (voice) — voice playback could trigger the remote avatar's talking animation
• Character picker, status surface, and anonymous session adoption #33 (character picker) — the picker shows local characters; this shows remote ones

Acceptance criteria

• When a clanker-to-clanker session is active, both avatars are visible in the TUI
• Remote avatar animates appropriately (talking when the remote agent is responding, idle otherwise)
• Remote agent's name is displayed alongside its avatar
• Fallback behavior works when remote avatar is unavailable
• Does not regress single-agent TUI layout