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/src/api/landing.rs

@@ -6,6 +6,8 @@
 //! `from` query parameter (the inviting admin's display name, set by E-12's link) is only passed on into the
 //! `kvitt://invite` link, never shown. Any code of 1 to 32 characters gets 200; anything else a 404 page.
 
+use std::fmt::Write as _;
+
 use axum::extract::{Path, RawQuery, State};
 use axum::http::{HeaderMap, HeaderValue, StatusCode, header};
 use axum::response::{IntoResponse, Response};
@@ -153,10 +155,11 @@ pub fn render(
         utf8_percent_encode(&code, NON_ALPHANUMERIC)
     );
     if let Some(name) = from {
-        open_url.push_str(&format!(
+        let _ = write!(
+            open_url,
             "&{FROM_PARAM}={}",
             utf8_percent_encode(name, NON_ALPHANUMERIC)
-        ));
+        );
     }
     let download = download_url
         .map(|url| {

server/crates/kvitt-server/src/api/rows.rs

@@ -22,8 +22,8 @@ pub fn uuid(text: &str) -> Result<Uuid, AppError> {
     Uuid::parse_str(text).map_err(|e| AppError::internal(format!("stored id is not a uuid: {e}")))
 }
 
-fn opt_uuid(text: Option<String>) -> Result<Option<Uuid>, AppError> {
-    text.as_deref().map(uuid).transpose()
+fn opt_uuid(text: Option<&str>) -> Result<Option<Uuid>, AppError> {
+    text.map(uuid).transpose()
 }
 
 /// Parses a stored snake_case enum token through its serde form.
@@ -504,7 +504,7 @@ pub async fn expense(conn: &mut SqliteConnection, id: Uuid) -> Result<Option<Exp
                 })
             })
             .collect::<Result<_, AppError>>()?,
-        recurring_template_id: opt_uuid(row.recurring_template_id)?,
+        recurring_template_id: opt_uuid(row.recurring_template_id.as_deref())?,
         recurring_period: row.recurring_period,
         created_by_user_id: uuid(&row.created_by_user_id)?,
         updated_by_user_id: uuid(&row.updated_by_user_id)?,