Redesign homepage and posts page layout

[x3ek]

Summary

Separate the homepage from the posts listing into two distinct pages with different purposes and layouts.

Current State

Currently, the homepage (index.html) is the posts listing — it shows the hero, then a card grid of all posts with pagination. This needs to split into two distinct pages.

Homepage (/) — evolves from current index.html

The current index.html template becomes the new homepage. It keeps its existing hero section but the post listing below it changes:

1. Hero section — site title, description, pixel art (existing, keep as-is)
2. Search bar — new, below the hero, prominent search input
3. Latest posts — new section showing the most recent posts (e.g., 3-5 cards)
4. Featured posts — new section with curated posts marked via featured: true frontmatter

Remove the current full post grid and pagination from the homepage — that moves to the dedicated posts page.

Posts Page (/posts) — new dedicated listing page

A new full browsing/filtering experience, built from scratch:

1. Search bar — at the top for keyword filtering
2. Sidebar — filter panel with:
   • Tag/label filter (checkbox or clickable tags)
   • Date range filter
3. Post cards — full-width cards (not grid), with more detail per post
4. Sorting — options for date (newest/oldest), or other criteria
5. Pagination — paged results

Theme Impact

• Each theme's index.html needs to be updated (hero stays, post grid replaced with latest + featured sections + search)
• A new posts listing template is needed (or index.html splits into index.html + posts.html)
• New template blocks or partials may be needed for the sidebar and search components
• The router may need changes to support the homepage vs posts page distinction, plus query params for filtering, sorting, and search

Dependencies

Blocked by:

• Navigation & Discovery: tag pages, archives, related posts #10 — Tag pages and tag infrastructure (needed for tag filtering in sidebar)
• Search functionality #11 — Search functionality (needed for search bar on both pages)
• Add featured post and page support #31 — Featured post and page support (needed for featured section on homepage)