feat(devkitd): migrate agent send to daemon lookup + client-side send #408

Part of the devkitd agent migration (#406). Model: daemon returns location data; client executes.

Scope

agent send <name> <msg> → daemon path:

• agent.lookup → runtimeRef; client sends via existing TS TmuxManager.sendKeys / herdr API — no daemon-side send RPC
• --stdin, --wait, --timeout, --json flags unchanged
• Fallback to sendAgentPrompt on unreachable/unknown-method

Depends on: agent.lookup (also used by kill/open) — implement once, reuse here.

Acceptance

• send reaches the correct pane/process via daemon-provided runtimeRef
• --wait response polling unchanged