fix: harden after-start prompt delivery

[nikhilachale]

Fixes #2517

Summary

• route spawn prompt handling through each agent adapter's prompt delivery strategy
• keep in-command prompts in argv and prevent an extra post-start send
• for after-start prompts, wait briefly for the TUI to settle, retry transport send failures, and tear down/terminate the partial spawn if delivery never succeeds

Tests

• go test ./internal/session_manager
• go test ./internal/adapters/agent/cline ./internal/adapters/agent/kimi
• env -u AO_SESSION_ID -u AO_PROJECT_ID -u AO_ISSUE_ID go test ./...

Notes

• A plain go test ./... in this AO worker shell fails in backend/internal/cli because inherited AO_SESSION_ID/AO_PROJECT_ID make project-context tests take the daemon lookup path. Clearing those AO context variables matches CI-style isolation and passes.