Replace weighted_sort

[beechnut]

Currently, projects have a weight attribute. This may have been used across the site at some point, but presently it's used in a single place: /our-work.

The effect of weighting projects and having a weighted sort is that it effectively pins certain projects.

The implementation is overly complex for the effect. But we do need the effect to remain consistent — the migration should result in no visible content changes.

I suspect the right way to do this is to:

• for the 6 projects with the highest weights, replace with pin: {rank, 1 being highest}
• run a pre-build validation that there are 6 pinned projects with unique numbers
• remove all other weight: attributes from the code
• update template code in /our-work to render all this correctly

### Acceptance criteria
- [ ] The same projects show up in /our-work
- [ ] There is documentation near the implementation that explains what it does

[edwintorres]

We're doing prioritization. We want to understand the impact of this issue.

[beechnut]

Okay so. This might be hard to explain in a single comment, but I'll give it a try.

EDIT: As far as impact — this will be important when we want to change the featured projects. Until then, not that important.

In the Jekyll site, there was a thing called weighted_sort that showed our six "most impactful" projects on /our-work, based off a per-project impact score called project_weight. But we don't sort ALL the projects by impact, we're just showing 6, so a whole scoring system for all our projects just to show a handful is over-engineering what could be a simple solution.

When we removed the weighted sorting algorithm, it didn't actually change which projects came out on top. The same projects are displayed.

For now.

But, as we add and remove projects over time, we will want to change which six projects we feature.

The work here should be, roughly, the following:

1. Remove the project_weight attribute from everything in content/projects/services/
2. Add pin: { number 1 through 6 } to the six pages currently being featured, for example, adding pin: 1 to projects/services/forest-service.md. The pin number would be the position in which the project appears in the featured project list in /our-work.
3. If possible, adding a validation that there are 6 project pages with unique numbers 1–6, and halting the build if not. This would prevent adding too many or too few pinned projects, and would require a specific order.
4. Change the project rendering in /our-work to:

-{% for case_study in featured.case_studies %}
-  {% assign project = collections.services | where: "data.agency", case_study.agency | first %}
-    {% include "card-project.html" project: project %}
+{% for project in collections.services | where: "data.pin" %} // or something like that
+    {% include "card-project.html", project: project %}