Import upstream v0.16.24, stripped

Upstream commit: af37a234981722493b74623a983581691d2b70b6
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
Renamed identifiers: 62 in 18 files
Verification: clean

The same Enterprise footprint as v0.16.23. The build check fails only on
tests/src/directory/issuer.rs, unchanged since v0.16.23: it calls a helper
from upstream's Enterprise-only OIDC test, and tests issuer-based directory
routing, an Enterprise feature. main has never carried it.

crates/jmap-proto/src/request/capability.rs

@@ -89,7 +89,7 @@ pub enum Capability {
     FileNode = 1 << 15,
     #[serde(rename(serialize = "urn:ietf:params:jmap:mail:share"))]
     MailShare = 1 << 16,
-    #[serde(rename(serialize = "urn:stalwart:jmap"))]
+    #[serde(rename(serialize = "urn:inbuxa:jmap:registry"))]
     Stalwart = 1 << 17,
     #[serde(rename(serialize = "urn:ietf:params:jmap:webpush-vapid"))]
     WebPushVapid = 1 << 18,
@@ -331,7 +331,7 @@ impl Capability {
             Capability::PrincipalsAvailability => "urn:ietf:params:jmap:principals:availability",
             Capability::FileNode => "urn:ietf:params:jmap:filenode",
             Capability::MailShare => "urn:ietf:params:jmap:mail:share",
-            Capability::Stalwart => "urn:stalwart:jmap",
+            Capability::Stalwart => "urn:inbuxa:jmap:registry",
             Capability::WebPushVapid => "urn:ietf:params:jmap:webpush-vapid",
             Capability::EmailPush => "urn:ietf:params:jmap:emailpush",
         }
@@ -477,7 +477,7 @@ impl Capability {
             "urn:ietf:params:jmap:contacts:parse" => Capability::ContactsParse,
             "urn:ietf:params:jmap:calendars:parse" => Capability::CalendarsParse,
             "urn:ietf:params:jmap:mail:share" => Capability::MailShare,
-            "urn:stalwart:jmap" => Capability::Stalwart,
+            "urn:inbuxa:jmap:registry" => Capability::Stalwart,
             "urn:ietf:params:jmap:webpush-vapid" => Capability::WebPushVapid,
             "urn:ietf:params:jmap:emailpush" => Capability::EmailPush,
         )

crates/jmap-proto/src/request/reference.rs

@@ -105,6 +105,12 @@ impl<V: Default> Default for MaybeResultReference<V> {
     }
 }
 
+impl<V: FromStr> Default for MaybeIdReference<V> {
+    fn default() -> Self {
+        MaybeIdReference::Invalid(String::new())
+    }
+}
+
 impl<T: Default> MaybeResultReference<T> {
     pub fn unwrap(self) -> T {
         match self {