Let the contracts assert properties, not the machine they were written on

The first run of the suite on a laptop found five contracts asserting the
desktop instead of the code. settings-system pinned DP-2 at 4500x3000 in
XRGB2101010; it now asks Hyprland what is actually primary. ssh-keys hardcoded
id_ed25519; it now uses whichever key exists. switcher's live half stepped a
session with one window, which step() deliberately refuses. displays raced the
service's revert readback -- the compositor looks restored while verification
still holds busy, so an immediate apply was refused with its error already
cleared; the harness now exposes settled and the contract waits for it.

declared-dependencies gets an OPTIONAL list for docker: the aliases serve
machines that run Docker deliberately, Panama's runtime is rootless podman,
and a missing docker fails by naming the command, which is loud enough.

Claude-Session: https://claude.ai/code/session_01Epx9ZC1gwm81K3jm9x9CKh

config/dot/quickshell/displays-harness.qml

@@ -32,7 +32,14 @@ ShellRoot {
                 canConfirm: Displays.canConfirm,
                 secondsLeft: Displays.secondsLeft,
                 lastError: Displays.lastError,
-                overridden: monitor ? Displays.isOverridden(monitor.name) : false
+                overridden: monitor ? Displays.isOverridden(monitor.name) : false,
+                // The compositor being visually restored is not the service
+                // being done: revert verification keeps its own readback
+                // running for a few ticks, and busy blocks a new apply until
+                // it settles. A caller that only watched `awaiting` raced
+                // this and got a refusal with no error text.
+                settled: !Displays.busy && !Displays.revertVerificationActive
+                    && !Displays.awaitingConfirmation
             });
         }