added device linking - #18

this lets you connect multiple computers and manage agents, chats, projects, files, and permitted terminals across them. one computer can connect to several hosts at once, several computers can connect to the same host, and a computer can do both. each computer connects outward to a relay, so they don't need the same network, tailscale, or port forwarding on the computers.

how it works:

• pair each computer with the hosts it needs through settings > devices. paste the host's invitation, compare the matching code, and approve access on that host. pairing with one host does not grant access to its other linked computers.
• each computer has its own identity. traffic between them uses encrypted tls 1.3 connections with certificate pinning. the relay forwards encrypted traffic without receiving the application data in plaintext.
• each host chooses read-only or full control for each approved computer, with a separate terminal permission. access can be revoked from the host.
• linked hosts open in separate windows with their own saved state. connections recover after interruptions without automatically repeating commands that may have already run.
• each computer can save 64 host links and 64 incoming approvals, with up to 16 simultaneous incoming connections per host.
• a self-hosted relay setup with docker compose and caddy is included. no public relay is configured by default, and each host computer needs to stay awake with the app running.

builds, targeted automated tests, and local desktop pairing, reconnection, and isolation checks pass. local desktop testing covered two instances. a larger group of physical computers, the full release gate, an actual docker deployment, and a pc-to-mac connection over the internet still need testing.

i don't expect you to use this 1:1, but i think it's a good baseline for supporting multiple devices.