Add CI lint configs (html-validate, linkinator), fix nav a11y and URL routing

- .htmlvalidate.json with relaxed rules for design-system inline styles
- linkinator.config.json skipping mail, external auth/platform origins
- Fix lint:html npm script quoting for Windows-shell compatibility
- Switch astro build.format to 'directory' so /pricing resolves without MultiViews
- trailingSlash: 'ignore' lets both /pricing and /pricing/ work naturally
- Add aria-label to both <nav> landmarks (Primary, Footer) to satisfy html-validate

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/components/SiteFooter.astro

@@ -14,7 +14,7 @@ const year = new Date().getFullYear();
       </svg>
       <span class="text-text-muted text-sm">© {year} Cameleer</span>
     </div>
-    <nav class="flex items-center gap-8 text-sm text-text-muted">
+    <nav class="flex items-center gap-8 text-sm text-text-muted" aria-label="Footer">
       <a href="/pricing" class="hover:text-text transition-colors">Pricing</a>
       <a href="/imprint" class="hover:text-text transition-colors">Imprint</a>
       <a href="/privacy" class="hover:text-text transition-colors">Privacy</a>

src/components/SiteHeader.astro

@@ -14,7 +14,7 @@ import CTAButtons from './CTAButtons.astro';
       </svg>
       <span class="font-sans font-bold text-lg tracking-tight text-text group-hover:text-accent transition-colors">Cameleer</span>
     </a>
-    <nav class="flex items-center gap-8 text-sm">
+    <nav class="flex items-center gap-8 text-sm" aria-label="Primary">
       <a href="/pricing" class="text-text-muted hover:text-text transition-colors">Pricing</a>
     </nav>
     <CTAButtons size="md" />