Packaging: the binary and package are inbuxa, INBUXA_* settings with STALWART_* fallback

- crates/main: package and [[bin]] renamed to inbuxa; homepage inbuxa.org;
  license AGPL-3.0-only (upstream is dual; the fork takes the AGPL).
- types::branding::env_var reads INBUXA_<name>, falling back to
  STALWART_<name> with a warning, for all nine server settings.
  STALWART_APP_ and STALWART_SPAM_* storage keys are unchanged.
- New-install default paths /var/lib/inbuxa and /var/log/inbuxa.
- Dockerfiles, systemd unit, launchd plist and AppArmor profile renamed.
- Upstream's .github moved to .github-upstream so none of it runs.
- install.sh stubbed: upstream's would install Stalwart.
- Two missed brand strings: the SMTP Received header and the utils user agent.

.github-upstream/ISSUE_TEMPLATE/config.yml

@@ -0,0 +1,17 @@
+blank_issues_enabled: false
+contact_links:
+  - name: Report an Issue
+    url: https://support.stalw.art
+    about: Report a potential bug at support.stalw.art. Confirmed bugs will be converted to Issues. Sign in with your GitHub account.
+  - name: Questions & Support
+    url: https://support.stalw.art
+    about: Get help with configuration, troubleshooting, or general questions at support.stalw.art. Sign in with your GitHub account.
+  - name: Feature Requests
+    url: https://support.stalw.art
+    about: Suggest new features or improvements at support.stalw.art. Sign in with your GitHub account.
+  - name: Join Stalwart's Reddit
+    url: https://www.reddit.com/r/stalwartlabs
+    about: Join our subreddit for community discussions and release announcements.
+  - name: Join Stalwart's Discord
+    url: https://discord.com/servers/stalwart-923615863037390889
+    about: Join our Discord server for community chat and release announcements.

.github-upstream/ISSUE_TEMPLATE/confirmed_issue.yml

@@ -0,0 +1,25 @@
+name: Bug Report (auto-closed)
+description: Issues opened here are automatically closed. Please report bugs at support.stalw.art instead.
+labels: ["bug"]
+title: "🪲: "
+body:
+  - type: markdown
+    attributes:
+      value: |
+        > [!CAUTION]
+        > **Issues opened directly in this repository are automatically closed and locked.**
+        >
+        > All bug reports must first be triaged at our support portal: **[support.stalw.art](https://support.stalw.art)**. If a maintainer confirms that your report is a genuine bug, they will create an Issue on your behalf; you do not need to (and should not) open one yourself.
+        >
+        > You can sign in to support.stalw.art with your existing GitHub account, so no separate registration is required.
+        >
+        > **What to do instead:**
+        > - Suspected bug, question, or feature request? Post it at [support.stalw.art](https://support.stalw.art).
+        >
+        > If you proceed and submit this form anyway, your issue will be closed automatically and a comment will be posted explaining this policy.
+  - type: checkboxes
+    attributes:
+      label: Acknowledgement
+      options:
+        - label: I understand that this issue will be automatically closed and that I should post my report at [support.stalw.art](https://support.stalw.art) instead.
+          required: true