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/test/java/com/m57/hermescontrol/E2eIntegrationTest.kt

@@ -958,14 +958,14 @@ class E2eIntegrationTest {
             coEvery { mockApiService.updateEnvVar(any()) } returns Response.success(Unit)
 
             val viewModel = KeysViewModel()
-            viewModel.loadKeys(reveal = false)
+            viewModel.loadKeys()
             advanceUntilIdle()
 
-            assertEquals(
-                "value1",
-                viewModel.uiState.value.envVars["KEY1"]
-                    ?.redactedValue,
-            )
+            val allVars =
+                viewModel.uiState.value.categories
+                    .flatMap { it.vars.entries }
+                    .associate { it.key to it.value }
+            assertEquals("value1", allVars["KEY1"]?.redactedValue)
 
             viewModel.updateKey("KEY1", "newValue")
             advanceUntilIdle()