T24e: Agent, environment

- SandboxStatus: a dot and a word (a ring while it starts or works), what it
  uses of what it has as meters, and how long it has run; the header wraps
- McpServerList over lists::ListItem: a dot per state, what it runs or why it
  failed, its tools once connected, and a switch
- ToolRegistry: tools grouped by source, found by every word of the owner's
  query, each Allow, Ask or Deny; rows wrap at 280px
- MemoryPanel: a line to keep a memory, Enter or Remember, blank words kept
  out; each memory with its source, when, and Forget
- CheckpointList over data_display::Timeline, newest first, the current point
  marked, Rewind on the rest
- gallery: every control wired to state

src/agent/tests/mod.rs

@@ -4,6 +4,7 @@ use gpui::{
 };
 
 mod changes;
+mod environment;
 mod previews;
 
 use super::{AgentProgress, Permission, PermissionPrompt, ToolApprovalDialog};