Resolves https://github.com/zed-industries/zed/issues/56138

This diff hides terminal agent actions from context menus shown by
embedded terminal views, such as terminal tool output in agent threads.
Those surfaces render through `TerminalView`, but they are not normal
interactive terminal panes, and actions like Inline Assist and Add to
Agent Thread do not currently resolve the embedded terminal as their
target.

Previously, choosing Inline Assist from terminal tool output could
target the workspace’s active editor instead of the terminal output. The
context menu now limits these agent actions to non-embedded terminal
views, so regular terminal panes keep their existing behavior while
terminal tool output no longer offers actions that cannot resolve to it.

Add to Agent Thread _could_ make sense for embedded terminal selections
in the future, but it would need explicit target-resolution support for
focused embedded terminals. This change keeps that as separate follow-up
work instead of leaving a misleading menu item that does not reliably
act on the selected tool output.

Release Notes:
- Fixed embedded terminal context menus showing agent actions that could
target the wrong item.