Improve performance on poor connections: local assets, gzip, caching

- Replace Tailwind CDN (~350KB) with purged local CSS (~22KB)
- Replace htmx unpkg CDN with local static file
- Add Gzip middleware (standard library, sync.Pool) for all responses
- Add Cache-Control: public, max-age=3600 for /static/* assets
- Reduce status polling interval from 5s to 30s
- Add scripts/build-css.sh for CSS regeneration after template changes
- Document in bible-local/operations.md and history.md

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

internal/middleware/static_cache.go

@@ -0,0 +1,19 @@
+package middleware
+
+import (
+	"strings"
+
+	"github.com/gin-gonic/gin"
+)
+
+// StaticCache sets Cache-Control headers for static assets (/static/*).
+// 1-hour cache allows browsers to reuse JS/CSS across page navigations
+// without re-downloading on every request.
+func StaticCache() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		if strings.HasPrefix(c.Request.URL.Path, "/static/") {
+			c.Header("Cache-Control", "public, max-age=3600")
+		}
+		c.Next()
+	}
+}