feat: complete contacts in the composer recipients

One shared QCompleter serves To, Cc and Bcc, attached with setWidget and
never setCompleter, which resets the prefix to the whole field and stops
matching after the first comma. The prefix is the comma-delimited token
under the cursor, set by hand from textEdited; accepting replaces only
that token and leaves the rest of the field alone.

Candidates match the name and the address case-insensitively. A display
name containing a comma is quoted on insertion, and splitRecipients() is
now quote-aware so the quoted name survives as one recipient.

Contacts reach the composer through setContacts() rather than a fourth
constructor argument, so every existing three-argument construction and
test stays as it was. An empty list leaves the fields behaving exactly
as before completion existed.

0 files changed, 0 insertions, 0 deletions