feat: prioritise sent-folder addresses in To/Cc/Bcc autocomplete (#380)

## What changed

`searchAddresses` (used by the To/Cc/Bcc autocomplete) now runs two passes over the candidate email rows:

1. **Sent-folder rows first** — the mailboxes table is queried for mailboxes with `role='sent'`; any email row whose `mailboxPath` matches gets processed before inbox/other rows. Within this group addresses are ordered by `receivedAt` DESC as before.
2. **All other rows** — processed after sent rows, also by `receivedAt` DESC.

Within sent-folder rows, `toAddresses` and `ccJson` are checked before `fromJson` (the sender in a sent email is our own address, not a useful suggestion). For non-sent rows the original order (`fromJson`, `toAddresses`, `ccJson`) is kept.

This means: if you wrote to `info@foo.de` yesterday and received spam from `info@spam.de` today, typing "i" surfaces `info@foo.de` first.

## How verified

- All 492 unit tests pass (`task test`).
- Added a dedicated test `searchAddresses prioritises sent-folder addresses over newer received` that inserts an older sent email and a newer received email matching the same query prefix and asserts the sent-folder address is returned first.

Closes #375

Co-authored-by: Thomas SharedInbox <sharedinbox@thomas-guettler.de>
Reviewed-on: https://codeberg.org/guettli/sharedinbox/pulls/380

test/unit/email_repository_impl_test.dart

@@ -497,6 +497,60 @@ void main() {
       },
     );
 
+    test(
+      'searchAddresses prioritises sent-folder addresses over newer received',
+      () async {
+        final r = _makeRepos();
+        await r.accounts.addAccount(_account, 'pw');
+
+        // Register the Sent mailbox so searchAddresses knows its role.
+        await r.db.into(r.db.mailboxes).insert(
+              MailboxesCompanion.insert(
+                id: 'acc-1:Sent',
+                accountId: 'acc-1',
+                path: 'Sent',
+                name: 'Sent',
+                role: const Value('sent'),
+              ),
+            );
+
+        // Older sent email: user deliberately wrote to info@foo.de.
+        await r.db.into(r.db.emails).insert(
+              EmailsCompanion.insert(
+                id: 'acc-1:sent-1',
+                accountId: 'acc-1',
+                mailboxPath: 'Sent',
+                uid: 1,
+                receivedAt: DateTime(2025),
+                toAddresses: const Value(
+                  '[{"name":"Foo","email":"info@foo.de"}]',
+                ),
+              ),
+            );
+
+        // Newer received email: spam arrived today from info@spam.de.
+        await r.db.into(r.db.emails).insert(
+              EmailsCompanion.insert(
+                id: 'acc-1:inbox-1',
+                accountId: 'acc-1',
+                mailboxPath: 'INBOX',
+                uid: 2,
+                receivedAt: DateTime(2026),
+                fromJson: const Value(
+                  '[{"name":"Spam","email":"info@spam.de"}]',
+                ),
+              ),
+            );
+
+        // Even though spam is newer, the sent-folder address should win.
+        final results = await r.emails.searchAddresses(null, 'info');
+        expect(results.map((a) => a.email).toList(), [
+          'info@foo.de',
+          'info@spam.de',
+        ]);
+      },
+    );
+
     // ── IMAP method tests ────────────────────────────────────────────────────
 
     test(