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-import/src/categories.rs

@@ -75,7 +75,7 @@ impl CategoryTable {
             else {
                 return Err(format!(
                     "category table: line {} must have three fields",
-                    record.position().map_or(0, |p| p.line())
+                    record.position().map_or(0, csv::Position::line)
                 ));
             };
             if name.trim().is_empty() || name.trim() != name {

server/crates/kvitt-import/src/plan.rs

@@ -249,12 +249,11 @@ fn plan_row(
     }
 
     let category = row.category.trim();
-    let category_key = match ctx.categories.lookup(category) {
-        Some(key) => key.to_owned(),
-        None => {
-            *unmapped.entry(category.to_owned()).or_insert(0) += 1;
-            FALLBACK_KEY.to_owned()
-        }
+    let category_key = if let Some(key) = ctx.categories.lookup(category) {
+        key.to_owned()
+    } else {
+        *unmapped.entry(category.to_owned()).or_insert(0) += 1;
+        FALLBACK_KEY.to_owned()
     };
     if description.is_empty() {
         return Err("empty description".into());