fix(composer): validate recipients

[FromSi]

What?

Added recipient validation in the composer for To, Cc, and Bcc fields.

• Validate email fields with mail.ParseAddress() when leaving a recipient field.
• Normalize display-name addresses to plain email addresses after validation.
• Clear inline validation errors when the user edits the field again.
• Block sending when recipient fields are invalid or when no recipients are provided.
• Show a composer notice for send-time validation problems.
• Added i18n keys for invalid recipient errors.

Why?

This prevents confusing SMTP failures caused by invalid recipient input and gives users immediate feedback inside the composer.

Closes #648
Closes #734

Testing

Added composer tests for:

• email list normalization;
• inline validation after leaving a recipient field;
• clearing validation errors when typing again;
• blocking send when a recipient field is invalid;
• blocking send when no recipients are provided;
• contact suggestion insertion behavior.

[FromSi]

@andriy-chernov need help with i18n

[FromSi]

@andrinoff Please double-check this FromOverride path for catch-all accounts. This value may not always be in the format expected by SMTP and could cause a syntax error like: 501 5.5.2 Syntax error, expected: MAIL FROM:<reverse-path> [parameters]. Thanks!

[andrinoff]

SMTP expects Name <email@something.com>.

for catch-all accounts, you can make a mistake there, yes.

You can add the check for it too, if you want. Just make sure to include that for accounts that do not have a name just@email.com is needed.

[FromSi]

Added 89c73b6

[andrinoff]

ill check everything out tomorrow, @mavonx, you too. crisis IRL

[andriy-chernov]

done, @andrinoff move the commit, please

[mavonx]

ill check everything out tomorrow, @mavonx, you too. crisis IRL

@andrinoff

Hope everything gets better soon.

[FromSi]

@andriy-chernov Sorry, I just noticed that the invalid_email_fields text was not quite right. It said “recipient”, but it should say “email” because the validation can also apply to the From field.

[andrinoff]

lgtm