fix(tui): Enter on selected session now enters session view

KeyResolver was swallowing Enter in IDLE state when input text was blank,
so SubmitInput never reached RootReducer to set sessionEntered=true.
Now Enter always dispatches SubmitInput in IDLE — RootReducer handles
blank text by entering the selected session, non-blank by starting a
new session (as before). IN_SESSION and FILTER mode unchanged (blank
Enter still returns null there).

apps/tui/src/main/kotlin/com/correx/apps/tui/input/KeyResolver.kt

@@ -40,7 +40,7 @@ object KeyResolver {
             DisplayState.IDLE -> when (key) {
                 KeyEvent.NavUp -> Action.NavigateUp
                 KeyEvent.NavDown -> Action.NavigateDown
-                KeyEvent.Enter -> if (inputText.isBlank()) null else Action.SubmitInput
+                KeyEvent.Enter -> Action.SubmitInput
                 KeyEvent.Tab -> Action.CycleMode
                 KeyEvent.Backspace -> Action.Backspace
                 KeyEvent.NewSession -> Action.OpenNewSessionPrompt

apps/tui/src/test/kotlin/com/correx/apps/tui/input/KeyResolverTest.kt

@@ -94,8 +94,8 @@ class KeyResolverTest {
     }
 
     @Test
-    fun `Enter in IDLE on blank input resolves to null`() {
-        assertNull(resolve(KeyEvent.Enter, DisplayState.IDLE))
+    fun `Enter in IDLE on blank input resolves to SubmitInput`() {
+        assertEquals(Action.SubmitInput, resolve(KeyEvent.Enter, DisplayState.IDLE))
     }
 
     @Test