refactor: group use cases into DDD bounded contexts

Flat use_cases/ (44 files) + monolithic commands.rs/queries.rs
split into diary/, movies/, watchlist/, import/, auth/, users/,
integrations/, search/, person/, federation/ — each with own
commands.rs, queries.rs, and use case modules.

Inline tests extracted to sibling tests/ dirs.

crates/application/src/integrations/get_tokens.rs

@@ -0,0 +1,11 @@
+use domain::{errors::DomainError, models::WebhookToken, value_objects::UserId};
+
+use crate::{context::AppContext, integrations::queries::GetWebhookTokensQuery};
+
+pub async fn execute(
+    ctx: &AppContext,
+    query: GetWebhookTokensQuery,
+) -> Result<Vec<WebhookToken>, DomainError> {
+    let user_id = UserId::from_uuid(query.user_id);
+    ctx.repos.webhook_token.list_by_user(&user_id).await
+}