feat(maestro): default structured view on for ACP agents

A Claude Code or Codex spawn now asks for the structured view unless the
operator says otherwise: the two spawn forms open with the box ticked and
`maestro spawn` takes `--terminal` to opt out. Once the operator works the
toggle, a command change no longer re-ticks it under them.

The support predicate moves to `maestro_protocol::display` so all three
clients gate on the same resolution.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

docs/STRUCTURED-VIEW.md

@@ -35,6 +35,22 @@ session's worktree holds unsaved work — applies to a structured session
 exactly as it does to a terminal one; only what gets terminated differs (an
 ACP handle instead of a tmux pane).
 
+## Choosing the view
+
+`view` is fixed at spawn and never changes. Every client picks it the same
+way, from the resolved command alone
+(`maestro_protocol::display::supports_structured_view`): a command that
+resolves to Claude Code or Codex spawns **Structured** by default, anything
+else spawns **Terminal**. The operator can override the default — the web and
+TUI spawn forms show the checkbox ticked and let it be unticked, and
+`maestro spawn` takes `--terminal` (or `--structured`, which sends the request
+even for a command the CLI does not recognise and lets the daemon refuse it).
+Once the operator works the toggle, a later command change never re-ticks it
+under them; it can still be forced off when the new command has no adapter.
+
+The daemon is the last word: a `Structured` request for a command with no
+adapter is refused there, whichever client sent it.
+
 ## The adapter
 
 The resolved structured command selects a provider adapter. Its binary is