chore: address PR feedback on domain migration

- Add distinctUntilChanged() to prevent duplicate emissions when
  DataStore write triggers re-collection (fixes Copilot review comment)
- Improve runBlocking comment to explain why it's acceptable here:
  one-time migration, fast DataStore write, downstream deduplication
- Rename test from 'no repeated saves' to 'idempotent across multiple reads'
  to accurately reflect what the test verifies (fixes Copilot review comment)

Ref: https://github.com/usetrmnl/trmnl-android/pull/262
All 49 unit tests pass (0 failures, 0 errors)

app/src/main/java/ink/trmnl/android/data/TrmnlDeviceConfigDataStore.kt

@@ -294,8 +294,11 @@ class TrmnlDeviceConfigDataStore
                             "Migrating API base URL from ${config.apiBaseUrl} to $newUrl for TRMNL device",
                         )
                         val migratedConfig = config.copy(apiBaseUrl = newUrl)
-                        // Save the migrated config back to DataStore synchronously
-                        // Using runBlocking is acceptable here as this is a one-time migration
+                        // Persist the migrated config back to DataStore (one-time migration)
+                        // Note: Using runBlocking here as Flow.map doesn't support suspend operations.
+                        // This is acceptable because: (1) it's a one-time migration per user,
+                        // (2) DataStore writes are fast, and (3) distinctUntilChanged() below
+                        // prevents duplicate downstream emissions from the save triggering re-collection.
                         runBlocking {
                             saveDeviceConfig(migratedConfig)
                         }
@@ -303,7 +306,7 @@ class TrmnlDeviceConfigDataStore
                     } else {
                         config
                     }
-                }
+                }.distinctUntilChanged()
 
         /**
          * Saves the complete device configuration

app/src/test/java/ink/trmnl/android/data/TrmnlDeviceConfigDataStoreTest.kt

@@ -821,7 +821,7 @@ class TrmnlDeviceConfigDataStoreTest {
         }
 
     @Test
-    fun `deviceConfigFlow migration is idempotent - no repeated saves`() =
+    fun `deviceConfigFlow migration is idempotent across multiple reads`() =
         runTest {
             // Arrange
             val config =