feat(#776): pairing management screen (#791)

REST + Channels-style UI for DM pairing (list pending/approved, approve, revoke, clear).

Co-authored-by: M57 <hy4ri@users.noreply.github.com>

app/src/main/java/com/m57/hermescontrol/data/model/Pairing.kt

@@ -0,0 +1,46 @@
+package com.m57.hermescontrol.data.model
+
+import kotlinx.serialization.SerialName
+import kotlinx.serialization.Serializable
+
+/**
+ * DM pairing management (issue #776).
+ *
+ * Backend contract (hermes_cli/web_server.py + gateway/pairing.py):
+ * - `GET /api/pairing` → `{pending: [...], approved: [...]}`
+ * - Pending entries: `{platform, request_id, user_id, user_name, age_minutes}`
+ * - Approved entries: `{platform, user_id, user_name, approved_at}`
+ *
+ * Codes are stored hashed server-side and never returned; pending requests are
+ * approved by their `request_id` (the desktop dashboard does the same).
+ */
+@Serializable
+data class PairingResponse(
+    val pending: List<PairingItem> = emptyList(),
+    val approved: List<PairingItem> = emptyList(),
+)
+
+@Serializable
+data class PairingItem(
+    val platform: String,
+    @SerialName("request_id") val requestId: String? = null,
+    @SerialName("user_id") val userId: String? = null,
+    @SerialName("user_name") val userName: String? = null,
+    @SerialName("age_minutes") val ageMinutes: Int? = null,
+) {
+    /** Stable key for LazyColumn + per-item action state. */
+    fun key(): String = "${platform}_${requestId ?: userId ?: ""}"
+}
+
+@Serializable
+data class PairingApproveRequest(
+    val platform: String,
+    @SerialName("request_id") val requestId: String? = null,
+    val code: String? = null,
+)
+
+@Serializable
+data class PairingRevokeRequest(
+    val platform: String,
+    @SerialName("user_id") val userId: String,
+)