[FEATURE] In-session agent view (← navigation) should be scopeable to the current project

Preflight Checklist

• [x] I have searched existing requests and this feature hasn't been requested yet
• [x] This is a single feature request (not multiple features)

Problem Statement

When I open the agent view from within a running interactive session (via the ← back navigation), it always lists every background session across all my projects. There is no settings.json key, env var, or in-view toggle to scope it to the current project.

The shell entrypoint already supports scoping — claude agents --cwd . narrows the list to one project (v2.1.141+) — but that scoping is not available when the agent view is reached in-session via ←. The running session already knows its own working directory, so the information needed to filter is right there.

Proposed Solution

Any of the following would solve the problem:

1. Have the in-session agent view inherit the session's cwd and default to that project's sessions (with a toggle to expand to all).
2. Add an in-view keyboard toggle to filter "current project only" ↔ "all projects".
3. Add a settings.json key (e.g. agentView.defaultScope: "cwd" | "all") so users can choose the default.

Use Case Example

I run Claude in one repo and frequently pop into the agent view with ← to check on background work. I only care about this project's agents, but I have to scan a global list mixing every project on my machine — which gets noisy fast with several active repos.

Related Issues

• #60975 (allow specifying cwd when spawning/viewing agents)
• #61134 (group sessions by working directory)