feat(settings): report which saved keys need a restart

Every settings update answered with a bare success, so the console could not
tell a change that took effect at once from one written to the file that the
running program would keep ignoring until it was restarted — the listener
address, the storage paths, the Komari dashboard URL.

Classify the patch instead. config.RestartRequiredKeys expands a patch into the
dot-separated paths of its leaves and intersects them with the settings main
reads before it starts serving, and the settings endpoint returns that list as
data.restartRequired. It is a pure function of the patch, so UpdateSettings
keeps its signature and nothing else has to change; the write succeeds either
way, and the field only says which edits are not live.

Matching is by overlap rather than equality, so a patch that names a section —
replacing it, or deleting it with a null — reports the startup-only keys inside
it, while a sibling subtree like webhook.endpoints is not mistaken for
webhook.enabled.

The result is never nil, so an update with nothing to report serializes as []
rather than null and a client can iterate it without a guard.

The console reads the field in ConfigSection and warns instead of confirming,
naming the keys that are pending; Settings.vue's hints for the Komari URL, the
listen address and the storage paths now say which of their fields is affected
rather than labelling the whole card.

frontend/src/api/index.js

@@ -13,6 +13,10 @@ export const serverApi = {
 
 // /api/settings/get?type=… / /api/settings/set?type=…
 // get → { success, message, data: { config } }.
+// set → { success, message, data: { type, restartRequired } }, where
+//       restartRequired lists the keys the update changed that are only read at
+//       startup, so the caller can say which edits are not live yet. It is
+//       always an array, empty when the whole update took effect.
 // `type` is one of global | bot_user_config | bot_node_config.
 // For set, pass a partial object; a JSON null value removes that key.
 export const settingsApi = {