Add Flickr tag filtering for adding photos

[CloCkWeRX]

This change allows members to filter their Flickr photos by a specific tag when adding photos to Growstuff.

Key changes:

• MemberFlickr#flickr_photos now accepts an optional tags parameter. If provided, it uses flickr.photos.search (filtered to the current user) instead of the default photostream or photoset retrieval.
• PhotosController#retrieve_from_flickr extracts params[:tag] and passes it to the flickr_photos method.
• The "New Photo" view (app/views/photos/new.html.haml) now includes a text input field for searching by tag, alongside the existing photoset selection.
• Added a test case in spec/controllers/photos_controller_spec.rb to ensure the tag parameter is correctly extracted and passed to the model.

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PR created automatically by Jules for task 3395495860406820072 started by @CloCkWeRX

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