Add `action='react'` to `send_message` tool and expose `add_reaction`/
`remove_reaction` on the Photon adapter.
- Track latest inbound message id per chat (`_last_inbound_by_chat`,
bounded to 200 entries) so the agent can react without threading
message ids through tool calls
- New `add_reaction`/`remove_reaction` public methods on PhotonAdapter;
unlike the lifecycle tapbacks, these are not gated by PHOTON_REACTIONS
- `send_message` gains `action='react'` with `emoji` and optional
`message_id` params; resolves target via existing channel-directory
and home-channel logic; requires a live gateway adapter
156f4fba92