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/remote/HermesApiService.kt

@@ -73,6 +73,11 @@ import com.m57.hermescontrol.data.model.SkillHubUninstallRequest
 import com.m57.hermescontrol.data.model.SkillScanResponse
 import com.m57.hermescontrol.data.model.StatusResponse
 import com.m57.hermescontrol.data.model.SystemStatsResponse
+import com.m57.hermescontrol.data.model.TelegramOnboardingApplyRequest
+import com.m57.hermescontrol.data.model.TelegramOnboardingApplyResponse
+import com.m57.hermescontrol.data.model.TelegramOnboardingStartRequest
+import com.m57.hermescontrol.data.model.TelegramOnboardingStartResponse
+import com.m57.hermescontrol.data.model.TelegramOnboardingStatusResponse
 import com.m57.hermescontrol.data.model.ToggleSkillRequest
 import com.m57.hermescontrol.data.model.Toolset
 import com.m57.hermescontrol.data.model.ToolsetToggleRequest
@@ -499,6 +504,32 @@ interface HermesApiService {
         @Path("platform_id") platformId: String,
     ): Response<MessagingPlatformTestResult>
 
+    @DELETE("api/messaging/platforms/{platform_id}")
+    suspend fun removeMessagingPlatform(
+        @Path("platform_id") platformId: String,
+    ): Response<Unit>
+
+    @POST("api/messaging/telegram/onboarding/start")
+    suspend fun startTelegramOnboarding(
+        @Body body: TelegramOnboardingStartRequest,
+    ): Response<TelegramOnboardingStartResponse>
+
+    @GET("api/messaging/telegram/onboarding/{pairing_id}")
+    suspend fun getTelegramOnboardingStatus(
+        @Path("pairing_id") pairingId: String,
+    ): Response<TelegramOnboardingStatusResponse>
+
+    @POST("api/messaging/telegram/onboarding/{pairing_id}/apply")
+    suspend fun applyTelegramOnboarding(
+        @Path("pairing_id") pairingId: String,
+        @Body body: TelegramOnboardingApplyRequest,
+    ): Response<TelegramOnboardingApplyResponse>
+
+    @HTTP(method = "DELETE", path = "api/messaging/telegram/onboarding/{pairing_id}", hasBody = false)
+    suspend fun cancelTelegramOnboarding(
+        @Path("pairing_id") pairingId: String,
+    ): Response<Unit>
+
     @GET("api/env")
     suspend fun getEnvVars(): Response<Map<String, EnvVarConfig>>