Editor: font-size presets + image insert/export support

Two editor features that were in flight alongside the sound work:
- FontSize TipTap extension (rides on textStyle) with Small/Normal/Large/
  Title presets in the toolbar; StatusBar + CSS support
- Image handling: internal/images handler, upload route + config, client
  API, EditorCore wiring, and md/html/docx export support for images

Claude-Session: https://claude.ai/code/session_016Yr6jELuRc7hyzYLccQKZd

cmd/server/main.go

@@ -15,6 +15,7 @@ import (
 	"gitea.parodia.dev/drwily/petal/internal/config"
 	"gitea.parodia.dev/drwily/petal/internal/db"
 	"gitea.parodia.dev/drwily/petal/internal/docs"
+	"gitea.parodia.dev/drwily/petal/internal/images"
 	"gitea.parodia.dev/drwily/petal/internal/lexicon"
 	"gitea.parodia.dev/drwily/petal/internal/llm"
 	"gitea.parodia.dev/drwily/petal/internal/suggestions"
@@ -80,6 +81,13 @@ func main() {
 		lex := lexicon.NewHandler()
 		api.Mount("/word", lex.Routes())
 		api.Mount("/gloss", lex.GlossRoutes())
+
+		// Editor image uploads, stored on disk and served back by content hash.
+		imgHandler, err := images.New(cfg.ImageDir)
+		if err != nil {
+			log.Fatalf("image store: %v", err)
+		}
+		api.Mount("/images", imgHandler.Routes())
 	})
 
 	// Everything else: serve the embedded SPA (with index.html fallback for client routing).