feat(agents): enable ACP builtin agents for team mode via CLI fallback

[ChristianLuciani]

Remove team_capable_override: false from all builtin ACP agents so runtime inference decides team eligibility instead of a blanket block.

What changed from the first version

The original commit only fixed Pi. But migrations 023, 025, and 029 apply the same team_capable_override: false to ~20 agents — not just Pi. Every external ACP agent is blocked from team mode even though most can execute shell commands and would pass supports_team_cli_fallback().

The migration now removes the override for all builtin + acp agents, letting each agent's actual capabilities decide.

Why this is the correct default

The runtime inference already has the right gates:

• supports_team_mcp() — for agents with MCP transport (stdio/http)
• supports_team_cli_fallback() — for agents that can execute shell (true unless caps explicitly disable shell/cli)

Agents that later gain MCP support will automatically use the richer Mcp transport via team_tool_transport() with zero changes here.

Changes (5 files)

• Migration 031: json_remove on team_capable_override for all builtin ACP agents
• registry.rs test: assert!(pi.team_capable)
• pi_acp_agent_migration test: verify override is absent
• registry_npx_agents_migration test: same
• registry_binary_agents_migration test: same

Verification

cargo test -p aionui-db --test pi_acp_agent_migration        # ✅
cargo test -p aionui-db --test registry_npx_agents_migration   # ✅
cargo test -p aionui-db --test registry_binary_agents_migration # ✅
cargo test -p aionui-ai-agent --lib "pi_builtin"               # ✅