Refresh Books page: DP volumes, QuantMFR, improved card design

[mmcky]

Summary

Refreshes the Books page with improved layout, card design, and content organisation.

Content changes

• DP volumes split: Single DP entry expanded into Volume I (Finite States) and Volume II (General States), each with its own card
• QuantMFR added: Quant Macro Finance (Hansen, Sargent, Borovička) added as a community book in 2nd position, with cover art from the project page
• NEW badge: Shown on DP Vol II and QuantMFR — remove later by deleting new: true from the project frontmatter
• Authors separated: Each book now has a dedicated authors field rendered as a readable byline, distinct from the abstract

Layout & design changes

• Single unified list: All books (QuantEcon and community) rendered in one sorted list ordered by order field; QE watermark shown only on QuantEcon-category books
• Top-level navigation: Books promoted from Projects dropdown to top nav bar
• Smaller cards: Reduced padding and thumbnail size for a more compact listing
• Hover effect: Cards highlight with a light background on hover (no underline)
• Card thumbnails: Images scale naturally to width with align-self: flex-start to prevent flex stretch

Adding more books later

Create a new file in _projects/ with:

---
name: "Book Title"
authors: "Author Name"
description: "Abstract text only (no author prefix)."
link: https://example.com
image: cover-image.png
order: 5
type: book
category: community   # or: quantecon
new: true             # optional — remove once no longer new
---

Preview

Please review the /books/ page on the deploy preview.

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[Copilot]

Pull request overview

Refreshes the Jekyll Books page to better surface recent QuantEcon publications, add community-authored books, and promote Books to the top-level navigation.

Changes:

• Split Dynamic Programming into Volume I and Volume II (with a configurable “NEW” badge on Volume II).
• Add a Community Books section driven by _projects/ frontmatter (type: book, category, order), starting with Quant Macro Finance.
• Move “Books” from the Projects dropdown into the top navigation bar.

Reviewed changes

Copilot reviewed 7 out of 8 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
assets/main.scss	Adds styling for a “NEW” badge on book cards.
assets/img/books/quantmfr-image.svg	Adds a cover image asset for the new community book entry.
_projects/quantmfr.md	Adds a new community book entry (Quant Macro Finance).
_projects/networks.md	Updates metadata (description, order) and assigns category: quantecon.
_projects/dp.md	Renames DP to Volume I, updates description/order, assigns category: quantecon.
_projects/dp-vol2.md	Adds DP Volume II entry with new: true, order, and category.
_layouts/default.html	Promotes Books to a top-level nav item and removes it from Projects dropdown.
_layouts/books.html	Implements category-based book grouping and NEW badge rendering.

Comments suppressed due to low confidence (1)

_layouts/books.html:52

• In the Community Books loop, the markup similarly opens .project and .item-info but only closes one </div> before closing the link. Please explicitly close both .item-info and .project divs to keep the HTML well-formed and avoid unexpected layout issues when the template is modified later.

        <div class="project d-flex flex-column align-items-start">
          <div class="item-info d-flex">
            <div class="item-pic-books"><img src="/assets/img/books/{{ project.image }}"></div>
            <div class="item-title">
              <h3 class="name">{{ project.name }}</h3>
				<div class="item-desc">
					{{ project.description | markdownify }}
				</div>
			</div>
        </div>
      </a>