Enable FSRS by default

Make FSRS (Free Spaced Repetition Scheduler) enabled by default for new users and users who haven't explicitly configured it.

Changes:
- Add BoolKey::Fsrs to default-true boolean keys in Rust backend
- Set defaultValue to true for FSRS toggle in deck options UI

rslib/src/config/bool.rs

@@ -79,6 +79,7 @@ impl Collection {
             | BoolKey::RestorePositionReviewer
             | BoolKey::LoadBalancerEnabled
             | BoolKey::FsrsHealthCheck
+            | BoolKey::Fsrs
             | BoolKey::NormalizeNoteText => self.get_config_optional(key).unwrap_or(true),
 
             // other options default to false

ts/routes/deck-options/FsrsOptionsOuter.svelte

@@ -96,7 +96,7 @@ License: GNU AGPL, version 3 or later; http://www.gnu.org/licenses/agpl.html
     />
     <DynamicallySlottable slotHost={Item} {api}>
         <Item>
-            <SwitchRow bind:value={$fsrs} defaultValue={false}>
+            <SwitchRow bind:value={$fsrs} defaultValue={true}>
                 <SettingTitle
                     on:click={() =>
                         openHelpModal(Object.keys(settings).indexOf("fsrs"))}