fix: Fix proposal order issue on "recent"

[AyakorK]

🎩 Description

Fixes unstable/incorrect sort order on the public proposals index (?order=recent, az, za, etc.), which caused old proposals to sometimes appear ahead of much more recent ones.

Two separate bugs, both fixed:

1. The final re-ordering step in proposals_controller_extends.rb used position(id::text in '...') to preserve sort order after pagination. Since that's a plain substring match, a short ID (e.g. 133) that's a substring of a longer, more recent ID (e.g. 2133) gets sorted next to it, regardless of actual date. Replaced with array_position(...), which matches IDs exactly instead of as text.
2. None of the sort options (recent, most_voted, az, etc.) had a tie-breaker. When several proposals tie on the sorted column (same published_at from an import, several proposals with 0 votes, etc.), Postgres falls back to physical row order, which isn't stable. Added .order(id: :desc) as a tie-breaker via a prepended reorder.

Also found along the way: our ProposalsControllerExtends override was being silently overwritten on every request by decidim_awesome's MemoizeExtraFields concern. Switched it from include to prepend to fix that.

Testing

In rails console, on a Proposals component:

component = Decidim::Component.find(YOUR_COMPONENT_ID)

ActiveRecord::Base.connection.execute("SELECT setval('decidim_proposals_proposals_id_seq', 89)")
short_old = Decidim::Proposals::Proposal.new(component: component, title: { "en" => "AAA short old id" }, body: { "en" => "test" })
short_old.save!(validate: false)
short_old.update_columns(created_at: "2021-01-01".to_time, published_at: "2021-01-01".to_time)

ActiveRecord::Base.connection.execute("SELECT setval('decidim_proposals_proposals_id_seq', 899)")
long_recent = Decidim::Proposals::Proposal.new(component: component, title: { "en" => "ZZZ long recent id" }, body: { "en" => "test" })
long_recent.save!(validate: false)
long_recent.update_columns(created_at: Time.current, published_at: Time.current)

import_time = 3.years.ago
5.times do |i|
  p = Decidim::Proposals::Proposal.new(component: component, title: { "en" => "Tied import #{i}" }, body: { "en" => "test" })
  p.save!(validate: false)
  p.update_columns(created_at: import_time, published_at: import_time)
end

Expected, on /proposals?order=recent:

• Sort is chronological: "ZZZ long recent id" on top, "AAA short old id" near the bottom with the other 2021-dated content.
• Reloading the page repeatedly keeps the "Tied import" proposals in the same order every time.

Also check /proposals?order=az for tied/duplicate titles — order should stay stable across reloads.

📌 Related Issues

• Fixes https://github.com/orgs/OpenSourcePolitics/projects/26/views/1?pane=issue&itemId=211340855&issue=OpenSourcePolitics%7Cintern-tasks%7C466

Tasks

• Fix proposals controller extends
• Add new extends that adds a tie-breaker to the reorder method for all sort options