feat: Product page: add to list counter + appbar shadow

[g123k]

Hi everyone!

I know, I know, this PR is only details…
But there's now a shadow below the AppBar when scrolling:

 

In the action bar, the icon next to "Add to a list" will show the number of lists:
 

When the Compare feature is disabled (incomplete product), the icon is crossed out:
 

A demo of the first two changes:
https://github.com/user-attachments/assets/b33115ee-2aa9-47e6-bc7a-1705b34b78f5

Note: I don't know why, but the file packages/smooth_app/lib/pages/product/product_page/new_product_footer.dart was not removed (fixed now ✅)

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 2.98507% with 65 lines in your changes missing coverage. Please review.

Project coverage is 6.83%. Comparing base (4d9c7fc) to head (ed26c4f).
Report is 481 commits behind head on develop.

Files with missing lines	Patch %	Lines
...t_page/footer/new_product_footer_add_to_lists.dart	0.00%	21 Missing ⚠️
packages/smooth_app/lib/resources/app_icons.dart	11.11%	16 Missing ⚠️
...roduct/product_page/footer/new_product_footer.dart	0.00%	14 Missing ⚠️
...pages/product/product_page/new_product_header.dart	0.00%	11 Missing ⚠️
...oth_app/lib/pages/product/product_list_helper.dart	0.00%	2 Missing ⚠️
...oduct_page/footer/new_product_footer_settings.dart	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           develop   #5869      +/-   ##
==========================================
- Coverage     9.54%   6.83%   -2.72%     
==========================================
  Files          325     428     +103     
  Lines        16411   23629    +7218     
==========================================
+ Hits          1567    1614      +47     
- Misses       14844   22015    +7171     

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[teolemon]

Sound good to me. The list counter is a nice touch, but we'll probably need a more visible option at some point.