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>

media/4ducky.css

@@ -0,0 +1,41 @@
+/* Additions for the Rust port. Everything else is the original styles_b.css / styles_fb.css. */
+
+/* styles_*.css say `width: 64x` (typo) - guest teaser images overflowed the grid. */
+#imageGrid div.b2 {
+	width: 64px;
+}
+
+/* textareas sized by cols= overflowed their box with wider fonts */
+#CommentForm textarea, #UForm textarea {
+	box-sizing: border-box;
+	width: calc(100% - 10px);
+}
+form.addComment textarea {
+	box-sizing: border-box;
+	max-width: calc(100% - 10px);
+}
+
+/* jQuery slimScroll replacement: thin, rounded, gray scrollbars. */
+div#rightpanel {
+	bottom: 0;
+	overflow-y: auto;
+	scrollbar-width: thin;
+	scrollbar-color: #555 transparent;
+}
+div#rightpanel::-webkit-scrollbar { width: 7px; }
+div#rightpanel::-webkit-scrollbar-thumb { background: #555; border-radius: 7px; }
+
+#spendenducks {
+	height: 190px;
+	width: 599px;
+	overflow-y: auto;
+	scrollbar-width: thin;
+	scrollbar-color: #555 transparent;
+}
+#spendenducks::-webkit-scrollbar { width: 7px; }
+#spendenducks::-webkit-scrollbar-thumb { background: #555; border-radius: 7px; }
+
+/* Links without href used to be href="javascript:;" */
+a[data-menu], a[data-toggle], a[data-fav], a[data-bbcode], a[data-admin], a[data-delcomment] {
+	cursor: pointer;
+}