AGPL source offer, notices and name cleanup

Every build writes the exact tree it was built from, uncommitted work
included, as source.tar.gz next to the app, and names that tree. The sidebar,
user menu, sign-in card and version tooltip link to it.

Coffey Labs' copyright line is added below Stalwart Labs' in every inherited
file changed, and the new files carry Coffey Labs' alone.

The upgrade prompt and its links are gone, the edition tooltip is neutral,
storage keys and the package description are INBUXA's own, and the README
states the lineage once, in the fine print.

README.md

@@ -7,19 +7,18 @@
 The administration interface for the INBUXA mail server: every server setting,
 first-boot setup, and recovery, in the browser.
 
-It is a fork of [Stalwart WebUI](https://github.com/stalwartlabs/webui). Like
-upstream it is schema-driven. After signing in it fetches the server's schema
-and builds every form, list and menu from it, so it covers every setting the
+It is schema-driven. After signing in it fetches the server's schema and
+builds every form, list and menu from it, so it covers every setting the
 server has without hardcoding any of them.
 
 > **Status: in development, not released.**
 
-## What's different from upstream
+## Design
 
-- **One edition.** Nothing is hidden or marked as Enterprise-only. INBUXA
-  ships every feature to everybody. See the INBUXA server's `docs/spec/`.
-- **Runs anywhere, not on the mail server.** Upstream is installed onto the
-  mail server itself. INBUXA Admin is its own deployment, pointed at the server
+- **One edition.** Every feature the server has is available here, with
+  nothing held back. See the INBUXA server's `docs/spec/`.
+- **Runs anywhere, not on the mail server.** INBUXA Admin is its own
+  deployment, never installed onto the mail server. It's pointed at the server
   either at build time (`VITE_API_BASE_URL`) or at deploy time:
   `<meta name="api-base-url" content="https://mail.example.com">` in
   `index.html`. Hosted like that, it signs in as the OAuth client
@@ -41,8 +40,8 @@ npm run build
 
 ## Keeping up with upstream
 
-Upstream's history contains no Enterprise-only code, so this is an ordinary
-git fork. `upstream` is a fetch-only remote:
+The upstream codebase's history contains no code under a proprietary license,
+so this is an ordinary git fork. `upstream` is a fetch-only remote:
 
 ```bash
 git fetch upstream --tags
@@ -52,13 +51,22 @@ git merge v1.0.12        # the next release tag
 ## Versions
 
 INBUXA Admin has its own dated version (`inbuxa-version.json`), shown with the
-WebUI release it's based on: `INBUXA Admin 2026.9.18 (WebUI 1.0.11)`.
+upstream release it's based on: `INBUXA Admin 2026.9.18 (base 1.0.11)`.
 `package.json` keeps upstream's version, so upstream's bumps merge cleanly.
 
+## Source code
+
+Every build carries its own source. The interface links to it (the user menu
+and the sign-in page), and the build writes it next to the app as
+`source.tar.gz`: the exact tree the running version was built from.
+
 ## License and credits
 
 Free software under the [GNU Affero General Public License, version 3](./LICENSES/AGPL-3.0-only.txt).
-A fork of Stalwart WebUI, copyright © Stalwart Labs LLC. Upstream's files are
-dual-licensed AGPL-3.0-only or Stalwart's Enterprise License, and INBUXA takes
-them under the AGPL-3.0 only. Upstream's copyright notices are kept on every
-file. INBUXA isn't affiliated with or endorsed by Stalwart Labs.
+
+INBUXA Admin is forked from the upstream AGPL-3.0 web administration codebase
+originally developed by Stalwart Labs. Their copyright notices are kept on
+every file inherited from it, and INBUXA's own notice is added to the files it
+changes. Those files are offered upstream under the AGPL-3.0-only or a
+proprietary license. INBUXA uses them under the AGPL-3.0 only. INBUXA isn't
+affiliated with or endorsed by Stalwart Labs.