Refresh site design, content, and layout

- New custom CSS design (dropped Bootstrap), redesigned footer
- Bigger, higher-resolution header logo
- Psychedelic hero background texture restored and credited (Jeremy Kun)
- Reorganized page sections (docs/discuss/source moved up, Sponsor/
  Enterprise grouped, History moved near the bottom, In Memory of
  Fredrik Lundh moved above the footer)
- New "From PIL to Pillow" history timeline with corrected/updated
  copy and styling
- Top nav merged into the header's upper-right actions (Project,
  Showcase, History + Sponsor button)
- Floating "back to top" button (site's first bit of JS), shows only
  while scrolling/near bottom
- Hero button copy/behavior fixes: "Download from PyPI" / "Read the
  docs" open in new tabs, Sponsor button links to #sponsor
- Responsive fixes: hero buttons no longer wrap awkwardly at
  ~860-1024px, stack cleanly on mobile
- Centered "Project" heading added above the docs/discuss/source list
- Misc copy tweaks and spacing/padding polish throughout

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Author: aclark4life

.pre-commit-config.yaml

@@ -0,0 +1,13 @@
+exclude: ^assets/fontawesome/
+
+repos:
+  - repo: https://github.com/pre-commit/pre-commit-hooks
+    rev: v5.0.0
+    hooks:
+      - id: trailing-whitespace
+      - id: end-of-file-fixer
+      - id: check-yaml
+      - id: check-json
+      - id: check-added-large-files
+      - id: check-merge-conflict
+      - id: mixed-line-ending