Add bins feature: upload, de-perspective, gallery

- lib/storage.mjs: bin CRUD with bin: prefix
- lib/grid-image.mjs: compute_bin_size() capped at 1024px
- server.mjs: POST/GET/PUT/DELETE /api/bins routes; PUT /api/bins/:id/corners
  re-processes image via process_grid_image with rows=1 cols=1
- public/lib/api.mjs: bin API wrappers including upload_bin()
- public/index.html: Bins nav button
- public/templates.html: t-section-bins, t-bin-card, t-dialog-bin-editor
- public/app.mjs: render_bins(), open_bin_editor() using Grid_Setup,
  save/cancel wiring in init()
- public/style.css: bin gallery and card styles

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

public/index.html

@@ -16,6 +16,7 @@
 			<button class="nav-btn" data-section="fields">Fields</button>
 			<button class="nav-btn" data-section="grids">Grids</button>
 			<button class="nav-btn" data-section="templates">Templates</button>
+			<button class="nav-btn" data-section="bins">Bins</button>
 		</nav>
 		<div class="maint-menu" id="maint-menu">
 			<button class="maint-toggle" id="maint-toggle" title="Maintenance">⚙</button>