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.

vendor/sieve-rs/VENDORED.md

@@ -0,0 +1,33 @@
+# sieve-rs, vendored
+
+The published [sieve-rs](https://crates.io/crates/sieve-rs) **0.7.3**, taken
+from crates.io under AGPL-3.0-only, with the upstream project's name taken
+out of the identifiers it spells into the Sieve language (docs/spec/SPEC.md
+§2.4). The root `Cargo.toml` patches it in with `[patch.crates-io]`.
+
+## Changes
+
+Every changed file carries the AGPL 5(a) notice in its header.
+
+- `src/compiler/grammar/mod.rs`: the extensions scripts `require` and
+  ManageSieve advertises are `vnd.inbuxa.while` and
+  `vnd.inbuxa.expressions`.
+- `src/runtime/mod.rs`: the default `environment "name"` is `inbuxa Sieve`
+  (the server sets its own name on both of its runtimes anyway), and the
+  test-only capability is `vnd.inbuxa.testsuite`.
+- `src/lib.rs`: the test-suite environment variables are `vnd.inbuxa.*`.
+- `Cargo.toml`: the example target is dropped, with the top-level
+  `examples/` and `tests/`, which the server never builds. (`src/` keeps its
+  own `tests` modules: the crate declares them.)
+
+## Updating
+
+When the server's `Cargo.lock` moves sieve-rs to a new version, Cargo stops
+using this copy and only warns that the patch went unused. The unit test
+`sieve_extensions_carry_the_fork_name` in `crates/common` fails when that
+happens. Re-vendor the new version from `~/.cargo/registry/src/*/sieve-rs-*`,
+dropping the top-level `tests/` and `examples/` (only those: `rsync
+--exclude /tests --exclude /examples`), `Cargo.lock` and `Cargo.toml.orig`, repeat
+the changes above, and update the version here and in the root `Cargo.toml`
+comment. `tools/fork/name-check.py` covers `vendor/` too, so a rename missed
+in a new version fails CI.