H3: retire manual harvest commands

Removes !forage / !mine / !scavenge / !fish / !essence / !commune from
the command surface. Typing one now returns a one-line deprecation DM
pointing at the auto-harvest flow ("Harvest is automatic now — just
walk."). The internal handleHarvestCmd / handleStandaloneHarvest paths
are left in place; operator deletes after soak per plan §H3.

Help text and the supplies-low autopilot pause line no longer mention
the manual verbs.

internal/plugin/dnd_r1_migration_test.go

@@ -163,7 +163,7 @@ func TestIsLegacyActivityInput(t *testing.T) {
 // and the harvest entry-points so the user has somewhere to go.
 func TestRenderLegacyActivityDeprecation(t *testing.T) {
 	out := renderLegacyActivityDeprecation(nil)
-	for _, want := range []string{"expedition", "!forage", "!mine", "retired"} {
+	for _, want := range []string{"expedition", "Harvest is automatic", "retired"} {
 		if !strings.Contains(out, want) {
 			t.Errorf("deprecation DM missing %q; got:\n%s", want, out)
 		}