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

website/index.html

@@ -690,7 +690,7 @@
                     </div>
                     <h3>Miners</h3>
                     <p>Learn mining, staking, and earning rewards</p>
-                    <a href="docs/docs-miners.html" class="doc-link">Miner Docs <i class="fas fa-arrow-right"></i></a>
+                    <a href="docs/miners.html" class="doc-link">Miner Docs <i class="fas fa-arrow-right"></i></a>
                 </div>
                 
                 <div class="doc-card">
@@ -699,7 +699,7 @@
                     </div>
                     <h3>Clients</h3>
                     <p>Use AITBC for AI/ML workloads</p>
-                    <a href="docs/docs-clients.html" class="doc-link">Client Docs <i class="fas fa-arrow-right"></i></a>
+                    <a href="docs/clients.html" class="doc-link">Client Docs <i class="fas fa-arrow-right"></i></a>
                 </div>
                 
                 <div class="doc-card">
@@ -708,7 +708,7 @@
                     </div>
                     <h3>Developers</h3>
                     <p>Build on AITBC and contribute</p>
-                    <a href="docs/docs-developers.html" class="doc-link">Developer Docs <i class="fas fa-arrow-right"></i></a>
+                    <a href="docs/developers.html" class="doc-link">Developer Docs <i class="fas fa-arrow-right"></i></a>
                 </div>
             </div>