perf: Add stable keys to Lazy list items for performance (#323)

Added stable `key` parameters to `items(...)` and `itemsIndexed(...)` calls across 13 screens. This prevents Compose from treating all list mutations as full item replacements and eliminates unnecessary full list recompositions during state updates.

Modifications applied to:
- KeysScreen.kt, SharedComponents.kt, AchievementsScreen.kt, PluginsScreen.kt
- SessionsScreen.kt, CronJobsScreen.kt, McpServersScreen.kt, PairingScreen.kt
- ToolsetsScreen.kt, ChatScreen.kt, ModelScreen.kt, SkillsScreen.kt
- KanbanScreen.kt, ProfilesScreen.kt, WebhooksScreen.kt

Note: LogsScreen.kt was left without a key because logs are string lines that can be duplicated, and using `.hashCode()` would cause a "Key was already used" crash. Positional indexing is safer there.

Fixes #279

app/src/main/java/com/m57/hermescontrol/ui/kanban/KanbanScreen.kt

@@ -149,7 +149,7 @@ fun KanbanScreen(
                                     contentPadding = PaddingValues(16.dp),
                                     horizontalArrangement = Arrangement.spacedBy(16.dp),
                                 ) {
-                                    items(state.columns) { column ->
+                                    items(state.columns, key = { it.name }) { column ->
                                         val colName = column.name
                                         val colTasks =
                                             filteredTasks.filter {
@@ -178,7 +178,7 @@ fun KanbanScreen(
                                                 modifier = Modifier.weight(1f),
                                                 verticalArrangement = Arrangement.spacedBy(8.dp),
                                             ) {
-                                                items(colTasks) { task ->
+                                                items(colTasks, key = { it.id }) { task ->
                                                     TaskCard(
                                                         task = task,
                                                         onMoveLeft =