Fix Insert-as-FX review findings: id rename, selection-count drift, refusal tooltip, success msg, master-only, reserve test

Renames the permanent action id out of the placement family, makes the button's
painted state and pressed outcome share one selection count, surfaces
panel-known refusals in the tooltip, reports the target track on success,
distinguishes a master-only selection, and pins the overflow-reserve test to the
real bar spec.

tests/test_insert_fx_enable.cpp

@@ -27,6 +27,18 @@ static void testEveryCombination() {
     CHECK(insertFxRefusal(3, true) == InsertFxRefusal::MultiCapture);
 }
 
+// GetSelectedTrack ignores the master track, so "only the master is selected" is a
+// distinct refusal from a plain empty selection -- both are !trackSelected, but the
+// message differs so a master-only user isn't told "select a track" when they did.
+static void testMasterOnlySelectedIsDistinctFromNoTrack() {
+    CHECK(insertFxRefusal(1, false, /*masterOnlySelected=*/true) ==
+          InsertFxRefusal::MasterOnlySelected);
+    CHECK(insertFxRefusal(1, false, /*masterOnlySelected=*/false) == InsertFxRefusal::NoTrack);
+    // The payload axis still runs first -- a bad capture count refuses on ITS reason
+    // even with the master selected.
+    CHECK(insertFxRefusal(0, false, /*masterOnlySelected=*/true) == InsertFxRefusal::NoCapture);
+}
+
 // Exactly one capture is the only count that can run; two is already too many.
 static void testOnlyASingleCaptureRuns() {
     CHECK(insertFxRefusal(2, true) == InsertFxRefusal::MultiCapture);
@@ -68,18 +80,24 @@ static void testEveryRefusalHasItsOwnSentence() {
     const std::string noCap = insertFxRefusalMessage(InsertFxRefusal::NoCapture);
     const std::string multi = insertFxRefusalMessage(InsertFxRefusal::MultiCapture);
     const std::string noTrk = insertFxRefusalMessage(InsertFxRefusal::NoTrack);
+    const std::string masterOnly = insertFxRefusalMessage(InsertFxRefusal::MasterOnlySelected);
 
     CHECK(none.empty());
     CHECK(!noCap.empty());
     CHECK(!multi.empty());
     CHECK(!noTrk.empty());
+    CHECK(!masterOnly.empty());
     CHECK(noCap != multi);
     CHECK(noCap != noTrk);
     CHECK(multi != noTrk);
+    CHECK(masterOnly != noTrk);
+    CHECK(masterOnly != noCap);
+    CHECK(masterOnly != multi);
 }
 
 int main() {
     testEveryCombination();
+    testMasterOnlySelectedIsDistinctFromNoTrack();
     testOnlyASingleCaptureRuns();
     testNegativeCountRefuses();
     testButtonBitIsThePayloadAxisOfTheFold();