Add Web Push, guided start screen, SVG icons, chunked uploads, rename

- Web Push (VAPID + RFC 8291, pure Rust): permission/question/finished
  notifications while no app window is visible; settings with test button
- Guided new-session flow: task, craft target (website/app/game/old
  software/fresh), clean room or deep, description, model, folder
  (new, existing or cloned git repository); originals upload to original/
- Craft phase bar (craft_phase tool) for study/specify/build/check/ready
- Chunked uploads (8 MB) up to server.max_upload_mb (default 500 MB)
- All UI glyphs and emojis replaced by themeable SVG icons
- Rename dialog with manual name or model-generated suggestion

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

web/src/components/ModelViewer.tsx

@@ -1,3 +1,4 @@
+import { Icon } from "./Icon";
 // 3D preview for GLB/GLTF, STL, OBJ and STEP/IGES (via OpenCascade WASM).
 // Loaded on demand only when such a file is opened.
 import { useEffect, useRef, useState } from "react";
@@ -147,7 +148,7 @@ export function ModelViewer({ url, ext }: { url: string; ext: string }) {
   return (
     <div className="model-viewer">
       <div ref={host} className="model-canvas" />
-      <div className="model-info">{state.loading ? "…" : state.error ? `⚠ ${state.error}` : state.info}</div>
+      <div className="model-info">{state.loading ? "…" : state.error ? <><Icon name="warning" /> {state.error}</> : state.info}</div>
     </div>
   );
 }