feat: implement shared-album multi-user photo album

Backend (Go/Gin/pgx): env config, pgx pool with retries, Garage S3 client
(path-style, region garage), embedded golang-migrate migrations, JWT auth with
refresh rotation, albums CRUD, members/roles/invites with no-escalation matrix,
photo upload + async imaging/goexif WebP variants, cursor pagination, presigned
URLs, likes/comments, SSE hub (album + personal), notifications, share links.

Frontend (SvelteKit 2 + Svelte 5 + Tailwind v4): API wrapper with 401 refresh,
auth store, all screens, Uploader/PhotoGrid/Lightbox/Comments, SSE client with
reconnect + REST catch-up, three themes + system via data-theme.

Deploy without Docker: Makefile builds the frontend into backend/static and
embeds it (go:embed) into a single statically linked binary; systemd unit and
nginx SSE example included.

Use gen2brain/webp (-tags nodynamic) instead of cgo kolesa-team/go-webp to keep
CGO_ENABLED=0 static builds; design.md/proposal.md updated accordingly.

frontend/src/app.html

@@ -0,0 +1,28 @@
+<!doctype html>
+<html lang="ru" data-theme="light">
+	<head>
+		<meta charset="utf-8" />
+		<meta name="viewport" content="width=device-width, initial-scale=1" />
+		<link rel="icon" href="%sveltekit.assets%/favicon.png" />
+		<script>
+			(function () {
+				try {
+					var stored = localStorage.getItem('theme') || 'system';
+					var resolved = stored;
+					if (stored === 'system') {
+						resolved = window.matchMedia('(prefers-color-scheme: dark)').matches
+							? 'dark'
+							: 'light';
+					}
+					document.documentElement.setAttribute('data-theme', resolved);
+				} catch (e) {
+					/* ignore */
+				}
+			})();
+		</script>
+		%sveltekit.head%
+	</head>
+	<body data-sveltekit-preload-data="hover">
+		<div style="display: contents">%sveltekit.body%</div>
+	</body>
+</html>