Add CI/CD pipelines, NSIS installer, ES module bundling, and ruff linting

- Add Gitea Actions workflows: test.yml (lint + test on push/PR) and
  release.yml (build + NSIS installer + upload on v* tags)
- Add NSIS installer with optional desktop shortcut and auto-start
- Add esbuild bundler: ES module migration with IIFE bundle output
- Add build-dist-windows.sh for cross-building Windows distribution
- Fix all ruff lint errors (import sorting, unused imports, line length)
- Remove redundant scripts (start-server.bat, stop-server.bat,
  start-server-background.vbs)
- Update CLAUDE.md with CI/CD and release documentation

media_server/static/js/background.js

@@ -2,6 +2,8 @@
 // Background: WebGL shader-based dynamic background
 // ============================================================
 
+import { frequencyData } from './player.js';
+
 let bgCanvas = null;
 let bgGL = null;
 let bgProgram = null;
@@ -216,7 +218,7 @@ function resizeBackgroundCanvas() {
 
 // ---- Cached color/theme updates (called on accent or theme change, not per-frame) ----
 
-function updateBackgroundColors() {
+export function updateBackgroundColors() {
     const style = getComputedStyle(document.documentElement);
     const accentHex = style.getPropertyValue('--accent').trim();
     if (accentHex && accentHex.length >= 7) {
@@ -245,8 +247,8 @@ function renderBackgroundFrame() {
 
     const time = performance.now() / 1000 - bgStartTime;
 
-    // Smooth audio data from the global frequencyData (shared with visualizer)
-    if (typeof frequencyData !== 'undefined' && frequencyData && frequencyData.frequencies) {
+    // Smooth audio data from the imported frequencyData (shared with visualizer)
+    if (frequencyData && frequencyData.frequencies) {
         const bins = frequencyData.frequencies;
         const step = Math.max(1, Math.floor(bins.length / BG_BAND_COUNT));
         for (let i = 0; i < BG_BAND_COUNT; i++) {
@@ -296,13 +298,13 @@ function stopBackground() {
 
 // ---- Public API ----
 
-function toggleDynamicBackground() {
+export function toggleDynamicBackground() {
     bgEnabled = !bgEnabled;
     localStorage.setItem('dynamicBackground', bgEnabled);
     applyDynamicBackground();
 }
 
-function applyDynamicBackground() {
+export function applyDynamicBackground() {
     const btn = document.getElementById('bgToggle');
     if (bgEnabled) {
         startBackground();