Per-device tokens with revocation (issue #11)

Auth previously used the shared IRIS_TOKEN as the security principal:
a leaked token meant access to all devices, and a compromised device
could not be isolated.

Gateway:
- pairing.py: devices.token column (in-place migration) + revoked
  denylist table; issue_token (idempotent, 64 hex), token_for,
  reissue_token, revoke/unrevoke/is_revoked/list_revoked. The token
  never leaks into device dicts (push fan-out / listings).
- http_server.py: auth accepts the shared token (bootstrap/legacy) OR
  the device's own token (both constant-time); a revoked device_id is
  rejected with 401 before either comparison. On SSE open (pairing)
  the per-device token is minted and returned in hello.ack.
- protocol.py: hello_ack(..., device_token).
- adapter.py: setup flow (hermes gateway setup -> Iris) now offers
  'Remove a paired device?' on an existing setup: numbered select
  menu (last option = exit the removal loop), confirmation, back to
  the menu for further removals.
- tools/iris_devices.py: operator CLI (list / revoke / unrevoke /
  reissue), stdlib only.

App:
- SecureStore.deviceToken (Android: EncryptedSharedPreferences;
  Desktop: second keyring slot iris-device-token / device_token.enc).
- HelloAckPayload.deviceToken; GatewayClient stores it on hello and
  presents it instead of the shared token from then on (live provider
  in HttpGateway); savePairing/clear wipe it for re-pairing.

Docs: 09 §9.3 stretch -> implemented (revocation semantics, both
control surfaces), 04 hello.ack example, frames.schema.json, M7 row 13.

Tests: 8 new Python tests (issuance, acceptance, revocation,
isolation, unrevoke, registry unit x2, setup-flow menu) - 94/94 pass;
2 new Kotlin wire tests - green. Live-verified against a running
gateway (hello.ack token matches devices.db; revoke -> 401 even with
shared token; unrevoke -> 200; setup TUI both paths).

app/shared/src/commonTest/kotlin/iris/protocol/HelloAckWireTest.kt

@@ -0,0 +1,31 @@
+package iris.protocol
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+/** Wire tests for the hello.ack payload (docs/04). */
+class HelloAckWireTest {
+    @Test
+    fun helloAckDeserializesDeviceToken() {
+        val raw =
+            """
+            {"v":1,"type":"hello.ack","payload":{"sync_cursor":5,
+              "last_pushed_cursor":3,"device_token":"9f2c64hex"}}
+            """.trimIndent()
+        val frame = IrisJson.instance.decodeFromString(Frame.serializer(), raw)
+        assertEquals("hello.ack", frame.type)
+        val p = frame.payloadAs<HelloAckPayload>()
+        assertEquals("9f2c64hex", p?.deviceToken)
+        assertEquals(5L, p?.syncCursor)
+        assertEquals(3L, p?.lastPushedCursor)
+    }
+
+    @Test
+    fun helloAckDefaultsDeviceTokenToEmpty() {
+        // Legacy gateways (pre per-device tokens) omit the field entirely.
+        val raw = """{"v":1,"type":"hello.ack","payload":{"sync_cursor":1}}"""
+        val frame = IrisJson.instance.decodeFromString(Frame.serializer(), raw)
+        val p = frame.payloadAs<HelloAckPayload>()
+        assertEquals("", p?.deviceToken)
+    }
+}