feat(oxibadge): cache employee names locally and let readers be a list

Employee names are now cached locally (employees.toml, keyed by reader
index then employee id) instead of being re-fetched from the time
clock on every month: load_employees only asks the device for ids not
already in the cache. When a month has employees the cache doesn't
know yet, a new screen (NewEmployees.svelte) lets the user name them
before continuing to the review screen; the chosen names are local to
Oxibadge only, never written back to the device. The same cache can be
managed afterwards from a drawer reachable from the time clock card in
Settings ("Gestisci dipendenti"), reusing the rename-in-row pattern
from the original mockup.

Settings.readers is a list again (was flattened to a single `reader`
object) so multiple time clocks can be supported later; only the first
one is used today.

Also:
- buildEmployees() now derives the employee list from the month's
  records instead of from every cached name ever seen, so the review
  screen no longer shows employees unrelated to the selected month.
- Renaming an employee from the review screen's pencil button now
  actually persists to the cache (the callback existed but was never
  wired up).
- Translated to English a number of Rust/TS/Svelte comments that had
  been written in Italian; only the i18n locale files should contain
  Italian.
- Minor dedup: extracted PillButton.svelte (was duplicated inline in
  ReaderCard), promoted the repeated .mono CSS rule to app.css, moved
  initials() out of the review feature into $lib/text.ts.

Assisted-by: Claude Sonnet 5 <noreply@anthropic.com>

oxibadge/src/lib/components/Onboarding.svelte

@@ -30,7 +30,7 @@
     try {
       await invoke('test_connection', { host: trimmedHost, port });
       const settings = await invoke<Settings>('load_settings');
-      await invoke('save_settings', { settings: { ...settings, reader: { host: trimmedHost, port } } });
+      await invoke('save_settings', { settings: { ...settings, readers: [{ host: trimmedHost, port }] } });
       onconnected({ host: trimmedHost, port });
     } catch (err) {
       setError(err);