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/cron/CronJobsScreen.kt

@@ -89,7 +89,7 @@ fun CronJobsScreen(
                     contentPadding = listContentPadding,
                     verticalArrangement = listItemSpacing,
                 ) {
-                    items(state.jobs) { job ->
+                    items(state.jobs, key = { it.id }) { job ->
                         Card(
                             modifier = Modifier.fillMaxWidth(),
                             colors =