Server overhaul: clear clippy::pedantic wins

Taken from a -W clippy::pedantic scan, no allow added: map_or/map_or_else, method references instead of closures,
clone_from, write! instead of push_str(format!), borrowed Option<&str>, push_of without a needless Option, the
envelope's entity moved instead of cloned, the scheduler's plan() no longer a needless async fn (its doc now says
what it does on failure), sort_unstable, digit separators and inline format args in tests. Not taken: missing
# Errors/# Panics docs, must_use, doc backticks, assert!(x.is_empty()) in tests, too_many_lines.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01TQd3pEP9UeN2uifbHknQ7B

server/crates/kvitt-server/tests/core_api/generation.rs

@@ -301,7 +301,14 @@ async fn an_existing_period_is_skipped_silently_by_the_unique_index() {
     let (id, _) = new_template(&app, json!({"day_of_month": 1, "start_period": "2026-11"})).await;
     // Another writer already created 2026-11 (as a racing scheduler run would).
     let other = app
-        .insert_expense(ACCOUNT_1, HOME, 1250000, ADMIN_ID, (750000, 500000), false)
+        .insert_expense(
+            ACCOUNT_1,
+            HOME,
+            1_250_000,
+            ADMIN_ID,
+            (750_000, 500_000),
+            false,
+        )
         .await;
     sqlx::query(
         "UPDATE expenses SET recurring_template_id = ?, recurring_period = '2026-11' WHERE id = ?",
@@ -469,7 +476,10 @@ async fn archived_account_continues_and_edits_affect_only_later_expenses() {
         dates(&generated(&app, id).await),
         ["2026-10-01", "2026-11-01"]
     );
-    assert_eq!(expense_of(&app, id, "2026-10").await["amount_ore"], 1250000);
+    assert_eq!(
+        expense_of(&app, id, "2026-10").await["amount_ore"],
+        1_250_000
+    );
     let november = expense_of(&app, id, "2026-11").await;
     assert_eq!(november["amount_ore"], 2000);
     assert_eq!(november["account_id"], ACCOUNT_1);

server/crates/kvitt-server/tests/core_api/logging.rs

@@ -81,7 +81,7 @@ async fn logs_hold_no_personal_content() {
             "/recurring-templates",
             &admin_token(),
             Some(template_body(json!({
-                "description": "Hemligbeskrivning", "notes": "Hemliganteckning", "amount_ore": 987654,
+                "description": "Hemligbeskrivning", "notes": "Hemliganteckning", "amount_ore": 987_654,
                 "day_of_month": 1, "start_period": "2026-09"
             }))),
         )

server/crates/kvitt-server/tests/core_api/rate_limit.rs

@@ -80,7 +80,7 @@ async fn unknown_tokens_count_against_the_ip_but_known_devices_keep_working() {
         200
     );
     for i in 0..60 {
-        let tok = format!("kvt_{:0>43}", i);
+        let tok = format!("kvt_{i:0>43}");
         let reply = app.send(from("192.0.2.1:1", None, "/me", Some(&tok))).await;
         assert_error(&reply, 401, "unauthorized");
     }