feat(#442): categorized env keys screen with add/remove, search, and gateway restart (#464)

* feat(#442): categorized env keys screen with add/remove, search, and gateway restart

- Group env vars by category (LLM Providers, Tool API Keys, Messaging
  Platforms, Agent Settings, Other) with collapsible AnimatedVisibility
  sections matching MCP screen pattern
- Add new env var form (PUT /api/env) with key/value inputs
- Delete env var via DELETE /api/env with EnvVarDeleteRequest body
- Reveal/hide/edit inline per-card controls
- Search bar filtering across key names and descriptions
- Gateway restart banner with one-click action when changes are dirty
- Track keysChanged flag showing restart prompt after mutations
- Wire delete endpoint in HermesApiService using @HTTP(hasBody=true)
- Add EnvVarDeleteRequest data model class

* fix(#442): update test to match new categorized KeysViewModel API

* fix(#442): satisfy ktlint multiline-expression-wrapping rule

---------

Co-authored-by: Hermes Agent <hermes@agent.local>

app/src/main/java/com/m57/hermescontrol/data/remote/HermesApiService.kt

@@ -24,6 +24,7 @@ import com.m57.hermescontrol.data.model.DebugShareResponse
 import com.m57.hermescontrol.data.model.DeleteWebhookResponse
 import com.m57.hermescontrol.data.model.DoctorResponse
 import com.m57.hermescontrol.data.model.EnvVarConfig
+import com.m57.hermescontrol.data.model.EnvVarDeleteRequest
 import com.m57.hermescontrol.data.model.EnvVarRevealRequest
 import com.m57.hermescontrol.data.model.EnvVarRevealResponse
 import com.m57.hermescontrol.data.model.EnvVarUpdate
@@ -87,6 +88,7 @@ import retrofit2.Response
 import retrofit2.http.Body
 import retrofit2.http.DELETE
 import retrofit2.http.GET
+import retrofit2.http.HTTP
 import retrofit2.http.PATCH
 import retrofit2.http.POST
 import retrofit2.http.PUT
@@ -482,6 +484,11 @@ interface HermesApiService {
         @Body request: EnvVarRevealRequest,
     ): Response<EnvVarRevealResponse>
 
+    @HTTP(method = "DELETE", path = "api/env", hasBody = true)
+    suspend fun deleteEnvVar(
+        @Body request: EnvVarDeleteRequest,
+    ): Response<Unit>
+
     @POST("api/ops/backup")
     suspend fun triggerBackup(): Response<ActionResponse>