[runtime] add progress and cancellation apis

[acrognale-oai]

Summary

• Add the app-facing runtime/install/progress notification and runtime/install/cancel request for the single active runtime installation, without introducing installation IDs.
• Move install orchestration into RuntimeInstallRequestProcessor, forward download/install phases to the requesting connection, support cancellation, and reuse an already-current runtime without downloading it again.
• Update the generated protocol surface and route runtime progress as a global notification in the TUI.
• The dependent remote-transport PR completes these lifecycle semantics for separated exec-server deployments and should land with this PR.

Test Plan

• Regenerated app-server schema fixtures; formatting and scoped Clippy checks passed.
• codex-app-server-protocol, codex-exec-server, and focused codex-app-server runtime-install tests passed.
• Focused codex-tui validation confirmed runtime progress notifications are routed globally.

Stack

1. #24111 - Introduce runtime/install API
2. #24112 - Add progress and cancellation APIs
3. #24113 - Forward runtime APIs from app-server to exec-server