Question: enable CLI-fallback team mode for Pi agent (team_capable_override)

First, thank you for AionCore — the architecture is impressive and the codebase is a pleasure to read.

## Context

I noticed the Pi agent (`backend: "pi"`, agent ID `484e4bf2`) cannot be used in team mode. The UI shows: "This assistant's agent does not support team mode."

Tracing through the code, I found the block is in the migration seed (`pi_acp_agent_migration.rs`):

```json
"behavior_policy": { "team_capable_override": false }
```

This forces `team_capable = false` in `registry.rs` regardless of what the ACP handshake reports:

```rust
let team_capable = behavior_policy.team_capable_override
.unwrap_or(inferred_team_capable);
```

The handshake from pi-acp reports `mcp_capabilities: { http: false, sse: false }` (no stdio), so `supports_team_mcp` correctly returns false. However, pi-acp does not declare `shell: false` or `cli: false`, which means it would pass `supports_team_cli_fallback` — Pi is a terminal-native agent that can execute shell commands.

## Question

Was `team_capable_override: false` set because the CLI fallback path would not actually work with pi-acp for a deeper reason (e.g., the team tool commands would not be interpretable by Pi over ACP), or was it a conservative default that could be relaxed?

If the CLI fallback would work, I would be happy to send a small PR to remove the override and update the corresponding test assertion. If there is a known blocker, I would rather understand it before going down the wrong path.

Thanks for your time!

Read pi_acp_agent_migration.rs and registry.rs, especially the team_capable_override handling and supports_team_cli_fallback path. Check the corresponding test assertion and determine whether removing the override makes Pi team-capable; done means the fallback behavior is confirmed and the test reflects the supported capability.

Written by the indexing model from the issue text.