Port 4ducky to Rust (Axum + SQLite)

Same design, layout, URLs and features as the PHP version: browse grid,
image view with AJAX comments, BBCode, likes, uploads (file, URL and
bookmarklet), quicktagger, profile, block list, inbox, invites, Hall of
Ducks, Truhe, abuse reports and the admin tools.

- Parameterized SQL, escaped templates (askama), argon2 passwords,
  server-side sessions, CSRF tokens on every write, strict script CSP
- SSRF-safe remote image fetching, magic-byte upload checks
- Self-hosted captcha replaces reCAPTCHA v1; analytics/social widgets removed
- Vanilla JS replaces jQuery and its plugins with the same DOM behaviour
- Reverse proxy support (frontend_path, trust_proxy, secure_cookies)
- Admin CLI: admin, settings, invites

See README.md for running it and the full list of changes.

Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>

templates/invites.html

@@ -0,0 +1,44 @@
+{% include "header.html" %}
+<div align="center">
+<form action="/login" method="post">
+	<fieldset>
+		<legend>Invites</legend>
+
+        <dl class="form">
+			<dt>Info:</dt>
+			<dd>
+				-Invitemissbrauch führt zum Ban. (Keine Reaktivierung) / Darunter fällt auch einem gebannten User einen Invite zu geben.
+			</dd>
+            <dt></dt>
+            <dd>-Nutzt die Invites weise. Baut euer Gast groben Unfug, seid ihr auch weg.</dd>
+            <dt>Howto:</dt>
+			<dd>Einfach den Link weiterschicken.</dd>
+         </dl>
+        <table class="table" width="100%" border="0" cellspacing="0">
+        	<tr class="tabletop">
+        		<td align="center" class="tabletoptd"><strong>InviteCode</strong></td>
+        		<td align="center" class="tabletoptd" width="100px"><strong>Used</strong></td>
+        	</tr>
+            {%- for i in invites %}
+				<tr class="tablelist">
+        		<td align="center" class="tabletd">
+					{%- if i.used_by.is_none() %}
+					<strong><a href="{{ l.frontend_path }}invites/{{ i.code }}">{{ i.code }}</a></strong>
+					{%- else %}
+					{{ i.code }}
+					{%- endif %}
+                    </td>
+        		<td align="center" class="tabletd" width="50px">{% if let Some(n) = i.used_by %}{{ n }}{% else %}no{% endif %}</td>
+        		</tr>
+            {%- else %}
+				<td align="center" class="tabletd">Zurzeit keine Invites für dich</td>
+                <td class="tabletd"></td>
+            {%- endfor %}
+
+            </table>
+
+	</fieldset>
+</form>
+</div>
+
+{% include "footer.html" %}