Replace remote search selects with static dropdowns on story admin form

[maebeale]

What is the goal of this PR and why is this important?

• The remote-select AJAX search for story author and spotlighted facilitator on the admin story form was unreliable
• Replace with static <select> dropdowns that load all available options upfront for a more dependable experience

How did you approach the change?

• Added @people and @users instance variables in StoriesController#set_form_variables with alphabetical ordering via Arel.sql
• @users loads all users with portal access, ordered by person name (nulls last) then email
• @people loads all people ordered by first/last name (case-insensitive)
• Replaced the remote-select Stimulus controller inputs with standard SimpleForm collection selects
• Applied custom caret styling helpers (select_caret_class, custom_caret_style, select_caret_onchange) consistent with other dropdowns in the form

UI Testing Checklist

• Navigate to admin story new/edit form
• Verify "Story author" dropdown populates with all users and is alphabetically sorted
• Verify "Story spotlighted facilitator" dropdown populates with all people and is alphabetically sorted
• Verify selecting an author and facilitator saves correctly
• Verify the caret styling updates on selection (gray when blank, dark when selected)

Anything else to add?

• This removes the dependency on the remote-select Stimulus controller for these two fields

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