Rename the identifiers that carried the upstream name

Everything clients, users and operators meet now carries the fork's name,
with no aliases (SPEC.md §2.4, changed here from "protocol identifiers
stay"):

- JMAP: upstream's registry capability is urn:inbuxa:jmap:registry, beside
  the fork's own urn:inbuxa:jmap.
- WebDAV lock and sync tokens are urn:inbuxa:dav*; clients resync once.
- Sieve: vnd.inbuxa.while and vnd.inbuxa.expressions. sieve-rs spells these
  into its compiler, so it's vendored (vendor/sieve-rs, 0.7.3) and patched in;
  a unit test fails if Cargo.lock ever moves past the vendored copy. The
  trusted runtime now names itself too, rather than answering sieve-rs's
  default.
- The web interface's OAuth client is inbuxa-webui. On every start the old
  stalwart-webui client is removed and any application naming it is moved
  over.
- The spam filter's blobs are INBUXA_SPAM_*; every start moves any left
  under the old keys, so a trained model survives.
- SQL stores and log files default to inbuxa, in the code and in the
  schema served to the admin (checksum regenerated).
- Settings are INBUXA_* only. A STALWART_* variable that's set where its
  INBUXA_* one isn't stops the server at startup, naming it.
- The version-upgrade messages link docs.inbuxa.org's migration page, and
  the OpenAPI description, smtp crate metadata and web-push test fixtures
  lose the name.

Kept on purpose, allowlisted with reasons: the OAuth key-derivation
contexts (renaming them would end every session and invalidate every
sealed client id) and the hashed application prefix.

Also fixes a latent start-up failure: ensure_client updated an existing
first-party client with a revision of 0, which the registry's assertion
never matches, so adding a redirect URI or changing the webmail secret
failed start-up. And the principal session test now expects
legacyProtocols (C-1, added 2026-09-21), which it had missed.

Tested: the server builds without warnings; common's 106 unit tests,
including the vendoring check; a new integration test for the two
start-up migrations; and the webdav, jmap, imap and SMTP Sieve suites.

crates/jmap/src/registry/mapping/bootstrap.rs

@@ -208,7 +208,7 @@ pub(crate) async fn bootstrap_set(
                         .with_description(concat!(
                             "The selected data store contains information from an older version. ",
                             "Please follow the upgrade instructions at ",
-                            "https://github.com/stalwartlabs/stalwart/blob/main/UPGRADING/v0_16.md"
+                            "https://docs.inbuxa.org/install/migrating/"
                         )),
                 );
                 break;
@@ -679,7 +679,7 @@ fn build_default_bootstrap(server: &Server) -> Bootstrap {
         directory: DirectoryBootstrap::Internal,
         tracer: Tracer::Log(TracerLog {
             path: "/var/log/inbuxa/".to_string(),
-            prefix: "stalwart".to_string(),
+            prefix: "inbuxa".to_string(),
             ansi: true,
             enable: true,
             ..Default::default()