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/gzip.go

@@ -0,0 +1,62 @@
+package middleware
+
+import (
+	"compress/gzip"
+	"strings"
+	"sync"
+
+	"github.com/gin-gonic/gin"
+)
+
+var gzPool = sync.Pool{
+	New: func() any {
+		w, _ := gzip.NewWriterLevel(nil, gzip.DefaultCompression)
+		return w
+	},
+}
+
+type gzResponseWriter struct {
+	gin.ResponseWriter
+	gz *gzip.Writer
+}
+
+func (w *gzResponseWriter) Write(data []byte) (int, error) {
+	return w.gz.Write(data)
+}
+
+func (w *gzResponseWriter) WriteString(s string) (int, error) {
+	return w.gz.Write([]byte(s))
+}
+
+func (w *gzResponseWriter) WriteHeader(code int) {
+	w.ResponseWriter.Header().Del("Content-Length")
+	w.ResponseWriter.WriteHeader(code)
+}
+
+// Gzip compresses all responses when the client sends Accept-Encoding: gzip.
+// Uses a pool of gzip writers to avoid per-request allocation overhead.
+func Gzip() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		if !strings.Contains(c.GetHeader("Accept-Encoding"), "gzip") {
+			c.Next()
+			return
+		}
+
+		orig := c.Writer
+		gz := gzPool.Get().(*gzip.Writer)
+		gz.Reset(orig) // compressed output goes into the original gin writer
+
+		c.Header("Content-Encoding", "gzip")
+		c.Header("Vary", "Accept-Encoding")
+		orig.Header().Del("Content-Length")
+
+		c.Writer = &gzResponseWriter{orig, gz}
+
+		defer func() {
+			gz.Close()
+			gzPool.Put(gz)
+		}()
+
+		c.Next()
+	}
+}

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()
+	}
+}