fix(web): chats are keyed on the agent's definition asset and send to its live run (CL-8441)

[TheGreatAxios]

Summary

• Chats are now keyed on an agent's definition asset id (joined from GET /workflows/deployments + GET /assets?kind=workflow), not a run id, so a hub restart's new anchor run no longer 409s an old chat.
• listChatAgents tracks, per agent, every address it has ever run under (releases included, so history survives redeploys) and its current live address (from a deployed/pending/recovering deployment), or null when none is live.
• Chat routes/keys/sidebar rows use the asset id; a chat's turns are every Sent/INBOX message whose participant address falls in that agent's address set.
• Sends resolve the live address at send time. When none is live, the composer shows " is starting…" (disabled) instead of erroring, and the relevant query polls every 3s until a live run appears.
• Composer default placeholder is "Message " (Myra by default).

Test plan

• bunx tsc -p apps/web --noEmit
• bun run fmt
• bun run lint
• bun run check (913 tests pass; e2e skipped, no DATABASE_URL)

[linear-code]

CL-8441