feat(pos): add PIN pad login page with keyboard support and theming

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

pos/static/css/common.css

@@ -0,0 +1,57 @@
+/* /home/Autopartes/pos/static/css/common.css */
+/* Theme variables — overridden by tenant theme */
+:root {
+    --color-primary: #1a73e8;
+    --color-secondary: #5f6368;
+    --color-accent: #ff6b35;
+    --color-bg: #ffffff;
+    --color-surface: #f8f9fa;
+    --color-text: #202124;
+    --color-text-secondary: #5f6368;
+    --color-border: #dadce0;
+    --color-success: #34a853;
+    --color-warning: #f9ab00;
+    --color-error: #ea4335;
+    --font-display: 'Sora', sans-serif;
+    --font-body: 'Plus Jakarta Sans', sans-serif;
+    --font-mono: 'JetBrains Mono', monospace;
+    --radius: 8px;
+    --shadow: 0 1px 3px rgba(0,0,0,0.12);
+}
+
+*, *::before, *::after { margin: 0; padding: 0; box-sizing: border-box; }
+
+body {
+    font-family: var(--font-body);
+    background: var(--color-bg);
+    color: var(--color-text);
+    line-height: 1.6;
+}
+
+.btn {
+    display: inline-flex;
+    align-items: center;
+    justify-content: center;
+    padding: 10px 20px;
+    border: 1px solid var(--color-border);
+    border-radius: var(--radius);
+    font-family: var(--font-body);
+    font-size: 0.95rem;
+    font-weight: 600;
+    cursor: pointer;
+    transition: all 0.2s;
+    background: var(--color-surface);
+    color: var(--color-text);
+}
+
+.btn:hover { background: var(--color-border); }
+.btn--primary { background: var(--color-primary); color: white; border-color: var(--color-primary); }
+.btn--primary:hover { opacity: 0.9; }
+.btn--accent { background: var(--color-accent); color: white; border-color: var(--color-accent); }
+
+.card {
+    background: var(--color-surface);
+    border: 1px solid var(--color-border);
+    border-radius: var(--radius);
+    padding: 24px;
+}