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/chat/ChatScreen.kt

@@ -715,7 +715,7 @@ private fun ChatInputBar(
                             LazyColumn(
                                 modifier = Modifier.heightIn(max = 200.dp),
                             ) {
-                                items(filteredCommands) { cmd ->
+                                items(filteredCommands, key = { it }) { cmd ->
                                     val description =
                                         when (cmd) {
                                             "/help" -> stringResource(R.string.command_help_desc)