Import upstream v0.16.23, stripped

Upstream commit: 9d1c75ab68435e4417337f768291e5f947686203
Enterprise-only files removed or emptied: 63
Enterprise-only snippets removed: 118 in 50 files
Dangling module declarations removed: 5
Edits turning enterprise off: 25
Third-party code: 14 files, 0 not in THIRD-PARTY.md
Verification: clean

One snippet more than v0.16.22, in crates/common/src/auth/authentication.rs
(3, was 2).

crates/main/Cargo.toml

@@ -7,7 +7,7 @@ homepage = "https://stalw.art"
 keywords = ["imap", "jmap", "smtp", "email", "mail", "webdav", "server"]
 categories = ["email"]
 license = "AGPL-3.0-only OR LicenseRef-SEL"
-version = "0.16.22"
+version = "0.16.23"
 edition = "2024"
 
 [[bin]]