Add contact antispam and fix gallery video playback.

English-only messages, rate limiting, min fill time, and normalized email
validation; improve modal video serving with posters, correct MIME types, and
no gzip on gallery media.

Co-authored-by: Cursor <cursoragent@cursor.com>

app/templates/contact.templ

@@ -4,7 +4,7 @@ templ ContactForm(enabled bool) {
 	<section id="contact" class="contact">
 		<h2>Contact</h2>
 		<p class="contact-intro">
-			Interested in a project or collaboration? Send a message below.
+			Interested in a project or collaboration? Send a message below. Messages must be in English.
 		</p>
 		if !enabled {
 			<p class="contact-unavailable">
@@ -33,7 +33,7 @@ templ ContactForm(enabled bool) {
 				</div>
 				<div class="form-row">
 					<label for="message">Message</label>
-					<textarea id="message" name="message" required rows="6" maxlength="8000"></textarea>
+					<textarea id="message" name="message" required minlength="20" rows="6" maxlength="8000" placeholder="Write at least a few sentences in English."></textarea>
 				</div>
 				<input
 					class="hp-field"
@@ -74,3 +74,9 @@ templ ContactSendError() {
 			<a href="mailto:hello@technical.kiwi">hello@technical.kiwi</a>.</p>
 	</div>
 }
+
+templ ContactRateLimited() {
+	<div class="alert alert-error" role="alert">
+		<p>Too many messages from your network. Please try again later.</p>
+	</div>
+}