Rename project from TopDeck to Canon

- Module github.com/cdnutter/canon, binary/command cmd/canon, Docker
  image and compose project "canon"
- Environment variables now use the CANON_ prefix
- Default site title is "<Your name>'s Canon" (or "Canon" with no name);
  a Site title set in Settings still overrides it
- Existing topdeck.db (and WAL files) is renamed to canon.db on start
- README: upgrade notes, including moving the old compose volume

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

internal/server/render.go

@@ -11,8 +11,8 @@ import (
 	"strconv"
 	"strings"
 
-	"github.com/cdnutter/topdeck/internal/store"
-	"github.com/cdnutter/topdeck/web"
+	"github.com/cdnutter/canon/internal/store"
+	"github.com/cdnutter/canon/web"
 )
 
 // Site is the owner-configurable identity shown on every page.
@@ -53,7 +53,7 @@ func (s *Server) site(ctx context.Context) Site {
 		ShowNotes:    set[store.SettingShowNotes] != "false",
 	}
 	if site.Title == "" {
-		site.Title = "TopDeck"
+		site.Title = DefaultTitle(site.OwnerName)
 	}
 	if !validTheme(site.Theme) {
 		site.Theme = DefaultTheme
@@ -71,6 +71,15 @@ func (s *Server) site(ctx context.Context) Site {
 	return site
 }
 
+// DefaultTitle is the site title when the owner hasn't set one:
+// "Chris's Canon", or just "Canon" before they've entered a name.
+func DefaultTitle(ownerName string) string {
+	if ownerName = strings.TrimSpace(ownerName); ownerName == "" {
+		return "Canon"
+	}
+	return ownerName + "'s Canon"
+}
+
 func (s *Server) handleCustomCSS(w http.ResponseWriter, r *http.Request) {
 	set, err := s.store.Settings(r.Context())
 	if err != nil {