refactor(applet): retire AliroApplet INS_EXCHANGE stub

The stub was added earlier this session as an X-CUBE-ALIRO compat
shim back when we (incorrectly) believed the vendor firmware ignored
the §10.2 step-up AID SELECT requirement and routed EXCHANGE directly
to the Expedited AID (ACCE5501). Today's Path X work proved the
vendor firmware actually DOES the §10.2 SELECT correctly once the
upstream crypto interop is right.

With M1B.1 / M1C.1 now landing the real EXCHANGE and ENVELOPE handlers
on StepUpApplet (ACCE5502), the AliroApplet stub is strictly wrong:
it would let stale expedited_device_counter state confuse the vendor
library if the reader ever hit it. Spec-conformant readers route
EXCHANGE to ACCE5502 after the step-up SELECT and never touch
ACCE5501 with INS=0xC9. So AliroApplet returns SW_INS_NOT_SUPPORTED
(0x6D00) for INS=0xC9 like any other unknown INS, and we ship one
less compat shim.

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

applet/src/test/java/com/dangerousthings/aliro/AliroAppletTest.java

@@ -92,4 +92,19 @@ class AliroAppletTest {
         assertEquals(0x01, versions[0] & 0xFF, "expected first protocol version high byte 0x01");
         assertEquals(0x00, versions[1] & 0xFF, "expected first protocol version low byte 0x00");
     }
+
+    @Test
+    void auth1ExchangeInsRejectedNowThatStepUpAppletOwnsIt() {
+        // Once M1B.1 / M1C.1 land StepUpApplet (ACCE5502) as the proper owner
+        // of INS_EXCHANGE (0xC9), AliroApplet must NOT also answer 0xC9 — a
+        // spec-conformant reader routes EXCHANGE to ACCE5502 after the §10.2
+        // step-up AID SELECT. AliroApplet receiving 0xC9 is a reader bug or
+        // a stale flow, and must be rejected with SW_INS_NOT_SUPPORTED so it
+        // can never accidentally interact with expedited session state.
+        selectExpedited();
+        CommandAPDU exchange = new CommandAPDU(0x80, 0xC9, 0x00, 0x00);
+        ResponseAPDU resp = sim.transmitCommand(exchange);
+        assertEquals(0x6D00, resp.getSW(),
+            "AliroApplet must reject INS_EXCHANGE (0xC9) — StepUpApplet (ACCE5502) owns it now");
+    }
 }