Multiple website improvements

[MDA2AV]

• docs/hugo.yaml — restructured navbar: Leaderboards, Simple Tests dropdown
  (Compliance/Smuggling/Malformed Input/Normalization), Sequence Tests dropdown
  (Coming Soon), Glossary, Add a Framework
• docs/assets/css/custom.css — removed vertical bar separators before Glossary
  and Add a Framework
• docs/content/_index.md — added Normalization card to landing page
• docs/content/add-a-framework/_index.md — documented 3 required endpoints
  (GET /, POST /, POST /echo) with full Flask example
• docs/content/probe-results/_index.md — added "Normalization" to the info
  callout
• docs/content/docs/_index.md — added Understanding HTTP card after RFC Basics
• docs/content/docs/baseline.md — weight 2 → 3
• 9 glossary section _index.md files — bumped weights (+2 each) to accommodate
  Understanding HTTP in sidebar order