Initial TopDeck: self-hosted ranked favorites

A single Go binary with SQLite that serves a public page of the owner's
ranked lists (movies, TV, albums, songs, video games, theater) and a
login-gated editor.

- Lists of 1–65,535 entries (100 recommended), several per category
- Search-to-add via TMDB, TheTVDB, IGDB, Deezer/MusicBrainz, Wikipedia;
  manual entry as a fallback
- Theater entries carry a production (Broadway, tour, …), venue and cast
- Artwork cached locally; URL override and uploads
- Drag, arrow and type-a-rank reordering; paginated for long lists
- 12 theme presets plus custom CSS
- First-run setup code or env-provided admin; bcrypt, rate-limited login,
  CSRF-guarded JSON API
- Dockerfile and docker-compose.yml

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

internal/server/themes.go

@@ -0,0 +1,35 @@
+package server
+
+// Theme is a built-in color preset. The actual colors live in
+// web/static/css/themes.css under [data-theme="<key>"].
+type Theme struct {
+	Key   string `json:"key"`
+	Label string `json:"label"`
+	Dark  bool   `json:"dark"`
+}
+
+var Themes = []Theme{
+	{"midnight", "Midnight", true},
+	{"obsidian", "Obsidian", true},
+	{"nord", "Nord", true},
+	{"dracula", "Dracula", true},
+	{"mocha", "Mocha", true},
+	{"rose-pine", "Rosé Pine", true},
+	{"gruvbox", "Gruvbox", true},
+	{"forest", "Forest", true},
+	{"synthwave", "Synthwave", true},
+	{"daylight", "Daylight", false},
+	{"paper", "Paper", false},
+	{"latte", "Latte", false},
+}
+
+const DefaultTheme = "midnight"
+
+func validTheme(key string) bool {
+	for _, t := range Themes {
+		if t.Key == key {
+			return true
+		}
+	}
+	return false
+}