Disambiguate program/engagement goals

[lelia]

From #26:

One thing that stood out while writing this is it's not clear what goals we are talking about. I think right now the section is providing both goals for the program as a whole as well as individual engagements.

We should take a second pass at revising /src/docs/goals.md and aim to distinguish between goals at both the program and engagement levels. Ultimately, it may make more sense to break out a separate "Program Goals" page under a different header, and keep the engagement-specific content in the original path.