refactor(docs): pivot to developer-first portal; archive legacy; fix MDX v3; update branding

  - Developer-first structure
      - Sidebar: keep only Overview and Developer; remove Vision from nav
      - Footer: add “Legal” with Terms/Privacy; remove duplicates
      - Developer Overview: correct internal links; Discord → https://discord.gg/srcful
  - Content updates
      - Overview: Grid Intelligence Layer, Connect with Sourceful, Zap as Connector
      - New: Zap for Developers (access pattern, data model overview, reliability, best practices)
      - Auth: clarify delegation, fix typos; add scopes example
      - Price API: fix slug to /developer/price-api; unit “MWh”; operator name
      - Data Models: fix slug to /developer/data-models
      - Design Manual: remove Team section
      - Core Principles: make equation runtime-safe (no MDX evaluation)
  - Branding and UX
      - Default dark mode; keep switch
      - Navbar logo: wide dark (light mode), wide teal (dark mode)
      - Consolidate legacy logo assets to static/img/archive
  - Build/config stability
      - MDX v3: ESM interop for remark-math/rehype-katex
      - KaTeX CSS → 0.16.10
      - Exclude docs/archive/** from docs build
      - Disable blog for a lean developer portal
  - Archival (preserved, hidden from nav)
      - Move to docs/archive: tokenomics, whitepaper, sustainability, helium-energy, getting-started, application-help-screens, _api-beta.md, beta-guide.md, guide.md,
  partners.md
  - Legal links unchanged
      - /sourceful-terms/terms and /sourceful-terms/privacy remain intact

Author: frahlg

.gitignore

@@ -18,3 +18,5 @@
 npm-debug.log*
 yarn-debug.log*
 yarn-error.log*
+writing
+AGENTS.md