Add tabbed sub-views to bins section, create-bin-from-source flow

Bins section now mirrors the grids section with two tabs:
- Bins: gallery of processed bin records
- Sources: source images tagged with uses=['bin'], with upload and
  '+ Bin' button to create a bin record from an existing source image

Server: POST /api/bins/from-source accepts source_id, creates bin
record and adds 'bin' to the source image's uses array.

URL state: /bins → bins tab, /bins/sources → sources tab.

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

public/lib/api.mjs

@@ -62,7 +62,8 @@ export async function upload_pdf(file, display_name, filename) {
 }
 
 // Bins
-export const get_bins        = () => req('GET', '/api/bins');
+export const get_bins            = () => req('GET', '/api/bins');
+export const create_bin_from_source = (source_id, name) => req('POST', '/api/bins/from-source', { source_id, name });
 export const get_bin         = (id) => req('GET', `/api/bins/${id}`);
 export const rename_bin      = (id, name) => req('PUT', `/api/bins/${id}`, { name });
 export const update_bin_corners = (id, corners) => req('PUT', `/api/bins/${id}/corners`, { corners });