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.

tools/fork/name-check.py

@@ -13,7 +13,8 @@ names, descriptions -- carries INBUXA's. Merging an upstream release brings
 new strings in with the name, and the merge itself can't tell, so this runs
 in CI on every push and pull request.
 
-Scope: string literals in `crates/**/*.rs`, test directories excluded.
+Scope: string literals in `crates/**/*.rs` and `vendor/**/*.rs`, test
+directories excluded.
 Comments are skipped, so copyright headers and doc comments never match.
 Some literals have to keep the name -- key-derivation contexts, wire-protocol
 identifiers, defaults that read an upstream installation -- and those are
@@ -79,8 +80,14 @@ def literals(src):
 
 def findings():
     found = set()
-    crates = os.path.join(ROOT, 'crates')
-    for dirpath, dirnames, filenames in os.walk(crates):
+    for top in ('crates', 'vendor'):
+        found |= findings_under(os.path.join(ROOT, top))
+    return found
+
+
+def findings_under(top):
+    found = set()
+    for dirpath, dirnames, filenames in os.walk(top):
         dirnames[:] = sorted(d for d in dirnames if d not in SKIP_DIRS)
         for f in sorted(filenames):
             if not f.endswith('.rs'):