feat(#443): Telegram onboarding, remove platform, credential expiry, field validation (#467)

* feat(#443): Telegram onboarding, remove platform, credential expiry, gateway command, field validation

- Add Telegram onboarding wizard: start (QR), poll status, cancel, apply
  with allowed-user-IDs flow. Full state machine in ChannelsViewModel.
- Add remove platform button with confirmation dialog (per card).
- Add credential expiry display in env var config fields.
- Add gateway_start_command to the offline banner with monospace hint.
- Add field validation for Slack token prefixes and member IDs.
- Add admin section showing env path and gateway command.
- Add DELETE, POST, GET API endpoints for onboarding + remove platform
  + action status polling.
- Extend MessagingPlatform model with envVar expiresAt, homeChannel,
  updatedAt fields.

* fix(#443): address review feedback + fix CI compilation & ktlint

- Remove duplicate getActionStatus overload (compilation blocker)
- Add missing Box import in ChannelsScreen (compilation blocker)
- Remove unused gatewayCommand param from AdminSection
- Centralize ISO timestamp parsing with UTC timezone
- Clean up WAITING phase dialog (remove redundant confirmButton)
- Use LocalHermesStatusColors for semantic surfaces
- Fix all ktlint violations in changed files

---------

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

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

@@ -14,6 +14,15 @@ data class MessagingPlatform(
     @SerializedName("error_code") val errorCode: String? = null,
     @SerializedName("error_message") val errorMessage: String? = null,
     @SerializedName("env_vars") val envVars: List<EnvVarField>? = null,
+    @SerializedName("updated_at") val updatedAt: String? = null,
+    @SerializedName("home_channel") val homeChannel: HomeChannelInfo? = null,
+)
+
+data class HomeChannelInfo(
+    val platform: String,
+    @SerializedName("chat_id") val chatId: String,
+    val name: String,
+    @SerializedName("thread_id") val threadId: String? = null,
 )
 
 data class EnvVarField(
@@ -27,6 +36,7 @@ data class EnvVarField(
     @SerializedName("is_password") val isPassword: Boolean,
     val advanced: Boolean = false,
     val url: String? = null,
+    @SerializedName("expires_at") val expiresAt: String? = null,
 )
 
 data class MessagingPlatformResponse(
@@ -47,3 +57,40 @@ data class MessagingPlatformTestResult(
     val state: String,
     val message: String,
 )
+
+// ── Telegram onboarding ─────────────────────────────────────────────────
+
+data class TelegramOnboardingStartRequest(
+    @SerializedName("bot_name") val botName: String = "Hermes Agent",
+)
+
+data class TelegramOnboardingStartResponse(
+    @SerializedName("pairing_id") val pairingId: String,
+    @SerializedName("suggested_username") val suggestedUsername: String,
+    @SerializedName("deep_link") val deepLink: String,
+    @SerializedName("qr_payload") val qrPayload: String,
+    @SerializedName("expires_at") val expiresAt: String,
+)
+
+data class TelegramOnboardingStatusResponse(
+    val status: String,
+    @SerializedName("bot_username") val botUsername: String? = null,
+    @SerializedName("owner_user_id") val ownerUserId: String? = null,
+    @SerializedName("expires_at") val expiresAt: String? = null,
+)
+
+data class TelegramOnboardingApplyRequest(
+    @SerializedName("allowed_user_ids") val allowedUserIds: List<String>,
+    val profile: String? = null,
+)
+
+data class TelegramOnboardingApplyResponse(
+    val ok: Boolean,
+    val platform: String,
+    @SerializedName("bot_username") val botUsername: String? = null,
+    @SerializedName("needs_restart") val needsRestart: Boolean,
+    @SerializedName("restart_started") val restartStarted: Boolean? = null,
+    @SerializedName("restart_action") val restartAction: String? = null,
+    @SerializedName("restart_pid") val restartPid: Int? = null,
+    @SerializedName("restart_error") val restartError: String? = null,
+)