feat: add llms.txt standard support for AI agent discoverability (#784)

Cherry-picked website/, scripts/generate-llms-full.sh, and deploy-docs.yml
from joyshmitz's PR. Fixed workflow to trigger on main branch instead of
docs/docusaurus-site.

Features:
- Docusaurus documentation site with llms.txt support
- Environment-variable driven config (defaults to steveyegge org)
- Automated llms-full.txt generation from docs
- GitHub Pages deployment workflow

Co-authored-by: joyshmitz <joyshmitz@users.noreply.github.com>

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Executed-By: beads/crew/dave
Rig: beads
Role: crew

website/static/img/favicon.svg

@@ -0,0 +1,4 @@
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+  <rect width="32" height="32" rx="6" fill="#25c2a0"/>
+  <text x="16" y="23" text-anchor="middle" font-family="system-ui, -apple-system, sans-serif" font-size="18" font-weight="700" fill="#ffffff">bd</text>
+</svg>

website/static/img/logo.svg

@@ -0,0 +1,4 @@
+<svg width="32" height="32" viewBox="0 0 32 32" xmlns="http://www.w3.org/2000/svg">
+  <rect width="32" height="32" rx="6" fill="#25c2a0"/>
+  <text x="16" y="23" text-anchor="middle" font-family="system-ui, -apple-system, sans-serif" font-size="18" font-weight="700" fill="#ffffff">bd</text>
+</svg>