docs: restructure website, optimize HTML, gitignore private files

Website docs (website/docs/):
- Delete 6 stale -md.html duplicates
- Rename docs-clients/miners/developers → clients/miners/developers.html
- Unify header/nav across all 15 pages (new .site-header pattern)
- Fix 34 dead href=# links with real targets
- Upgrade Font Awesome v4→v6 in index.html
- Replace search stub with live client-side search (15-page index)
- Extract all inline CSS into shared docs.css (+630 lines)
- Extract inline theme JS into shared theme.js
- Strip inline style= attributes from 10+ pages
- Add .announce-banner, .source-links, .search-results CSS classes
- Add Markdown Source links to clients/miners/developers pages
- Update components.html title to Architecture & Components
- Move browser-wallet.html to website/wallet/, leave redirect
- Update all dates to February 2026

Website root:
- Delete 6 root-level duplicate HTML files (160KB saved)
- Rewire index.html and 404.html links

Root README.md:
- Fix 8 broken doc links to new numbered folder structure
- Update copyright to 2026

.gitignore + .example files:
- Gitignore private files: .aitbc.yaml, .env, deploy scripts,
  GPU scripts, service scripts, infra configs, .windsurf/, website README
- Create 7 .example files for GitHub users with sanitized templates
- Untrack 47 previously committed private files

Live server:
- Push all website files to aitbc-cascade:/var/www/html/
- Clean stale admin.html and index.nginx-debian.html

scripts/gpu/gpu_registry_demo.py

@@ -1,72 +0,0 @@
-#!/usr/bin/env python3
-"""
-Simple GPU Registry Server for demonstration
-"""
-
-from fastapi import FastAPI, HTTPException
-from pydantic import BaseModel
-from typing import Dict, Any, Optional
-import uvicorn
-from datetime import datetime
-
-app = FastAPI(title="GPU Registry Demo")
-
-# In-memory storage
-registered_gpus: Dict[str, Dict] = {}
-
-class GPURegistration(BaseModel):
-    capabilities: Dict[str, Any]
-    concurrency: int = 1
-    region: Optional[str] = None
-
-class Heartbeat(BaseModel):
-    inflight: int = 0
-    status: str = "ONLINE"
-    metadata: Dict[str, Any] = {}
-
-@app.get("/")
-async def root():
-    return {"message": "GPU Registry Demo", "registered_gpus": len(registered_gpus)}
-
-@app.get("/health")
-async def health():
-    return {"status": "ok"}
-
-@app.post("/miners/register")
-async def register_gpu(miner_id: str, gpu_data: GPURegistration):
-    """Register a GPU miner"""
-    registered_gpus[miner_id] = {
-        "id": miner_id,
-        "registered_at": datetime.utcnow().isoformat(),
-        "last_heartbeat": datetime.utcnow().isoformat(),
-        **gpu_data.dict()
-    }
-    return {"status": "ok", "message": f"GPU {miner_id} registered successfully"}
-
-@app.post("/miners/heartbeat")
-async def heartbeat(miner_id: str, heartbeat_data: Heartbeat):
-    """Receive heartbeat from GPU miner"""
-    if miner_id not in registered_gpus:
-        raise HTTPException(status_code=404, detail="GPU not registered")
-    
-    registered_gpus[miner_id]["last_heartbeat"] = datetime.utcnow().isoformat()
-    registered_gpus[miner_id]["status"] = heartbeat_data.status
-    registered_gpus[miner_id]["metadata"] = heartbeat_data.metadata
-    
-    return {"status": "ok"}
-
-@app.get("/miners/list")
-async def list_gpus():
-    """List all registered GPUs"""
-    return {"gpus": list(registered_gpus.values())}
-
-@app.get("/miners/{miner_id}")
-async def get_gpu(miner_id: str):
-    """Get details of a specific GPU"""
-    if miner_id not in registered_gpus:
-        raise HTTPException(status_code=404, detail="GPU not registered")
-    return registered_gpus[miner_id]
-
-if __name__ == "__main__":
-    print("Starting GPU Registry Demo on http://localhost:8091")
-    uvicorn.run(app, host="0.0.0.0", port=8091)