Optional app PIN, settings header, pink selection ring

- A PIN (4 to 8 digits, salted SHA-256 in prefs) set in Settings shows
  a logo splash with a PIN prompt at start and whenever the app returns
  after leaving the screen; Back there leaves the app.
- Settings gets the back-arrow header shared with the folder grid
  (Ui.header) and scrolls, since the PIN fields overflow the screen.
- Tile and list focus rings use the icon pink.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

1 files changed, 19 insertions, 0 deletions

diff --git a/app/src/test/java/mygram/droid/LogicTest.java b/app/src/test/java/mygram/droid/LogicTest.java
index e807725..6fb45aa 100644
--- a/app/src/test/java/mygram/droid/LogicTest.java
+++ b/app/src/test/java/mygram/droid/LogicTest.java
@@ -107,4 +107,23 @@ public class LogicTest {
 		assertFalse(d.press(2000));
 		assertFalse("301 ms is too slow", d.press(2301));
 	}
+
+	@Test
+	public void validatesPins() {
+		assertTrue(Prefs.validPin("1234"));
+		assertTrue(Prefs.validPin("12345678"));
+		assertFalse(Prefs.validPin("123"));
+		assertFalse(Prefs.validPin("123456789"));
+		assertFalse(Prefs.validPin("12a4"));
+		assertFalse(Prefs.validPin(""));
+	}
+
+	@Test
+	public void hashesPinsWithSalt() {
+		String h = Prefs.hash("00ff", "1234");
+		assertEquals(64, h.length());
+		assertEquals(h, Prefs.hash("00ff", "1234"));
+		assertFalse(h.equals(Prefs.hash("00fe", "1234")));
+		assertFalse(h.equals(Prefs.hash("00ff", "1235")));
+	}
 }