feat: harden Flow cold-start/force-quit and polish macOS dictation UX

Fix cold-start overlay recursion that overflowed the main-thread stack when
recording began while the ready overlay was still up; also remove temporary
on-screen Flow DEBUG panels after the orange-mic investigation, and land the
macOS overlay/catalog/layout polish plus related Flow recovery hardening.

OSGKeyboardTests/IntelligentPolishTests.swift

@@ -340,7 +340,7 @@ final class IntelligentPolishTests: XCTestCase {
 
     @MainActor
     func testFlowFallbackDeliveryCleansTextAndCarriesWeakNetworkWarning() {
-        let delivery = FlowSessionManager.makeFallbackDelivery(
+        let delivery = TranscriptionPolishFallback.makeDelivery(
             rawText: "  你 是不是 已经 解决了 这个 问题 ？  ",
             error: LLMError.transport("offline"),
             engineMode: "cloud",
@@ -352,6 +352,20 @@ final class IntelligentPolishTests: XCTestCase {
         XCTAssertEqual(delivery.polishWarning, SharedL10n.string("flow.warning.polishDegraded"))
     }
 
+    func testTranscriptionPolishFallbackLocalMissingKeyWarning() {
+        let delivery = TranscriptionPolishFallback.makeDelivery(
+            rawText: "测试文本",
+            error: PolishingService.PolishError.missingAPIKey,
+            engineMode: "local",
+            chunkWarning: nil
+        )
+        XCTAssertEqual(delivery.text, "测试文本")
+        XCTAssertEqual(
+            delivery.polishWarning,
+            SharedL10n.string("flow.warning.localPolishUnavailable")
+        )
+    }
+
     func testHasStructureSignalDetectsChineseEnumeration() {
         XCTAssertTrue(TranscriptPostProcessor.hasStructureSignal(in: "首先测试其次上线"))
         XCTAssertTrue(TranscriptPostProcessor.hasStructureSignal(in: "第一点修复"))