feat: Minify css

- Add dependency clean-css
- Add do_minifycss function as filter to eleventy
- Add workaround for demo mode with computed data file

package-lock.json

@@ -10,6 +10,7 @@
       "license": "MIT",
       "devDependencies": {
         "@11ty/eleventy": "^2.0.1",
+        "clean-css": "^5.3.3",
         "sass": "^1.69.4"
       }
     },
@@ -539,6 +540,18 @@
         "fsevents": "~2.3.2"
       }
     },
+    "node_modules/clean-css": {
+      "version": "5.3.3",
+      "resolved": "https://registry.npmjs.org/clean-css/-/clean-css-5.3.3.tgz",
+      "integrity": "sha512-D5J+kHaVb/wKSFcyyV75uCn8fiY4sV38XJoe4CUyGQ+mOU/fMVYUdH1hJC+CJQ5uY3EnW27SbJYS4X8BiLrAFg==",
+      "dev": true,
+      "dependencies": {
+        "source-map": "~0.6.0"
+      },
+      "engines": {
+        "node": ">= 10.0"
+      }
+    },
     "node_modules/color-convert": {
       "version": "2.0.1",
       "resolved": "https://registry.npmjs.org/color-convert/-/color-convert-2.0.1.tgz",
@@ -583,9 +596,9 @@
       }
     },
     "node_modules/cross-spawn": {
-      "version": "7.0.3",
-      "resolved": "https://registry.npmjs.org/cross-spawn/-/cross-spawn-7.0.3.tgz",
-      "integrity": "sha512-iRDPJKUPVEND7dHPO8rkbOnPpyDygcDFtWjpeWNCgy8WP2rXcxXL8TskReQl6OrB2G7+UJrags1q15Fudc7G6w==",
+      "version": "7.0.6",
+      "resolved": "https://registry.npmjs.org/cross-spawn/-/cross-spawn-7.0.6.tgz",
+      "integrity": "sha512-uV2QOWP2nWzsy2aMp8aRibhi9dlzF5Hgh5SHaB9OiTGEyDTiJJyx0uy51QXdyWbtAHNua4XJzUKca3OzKUd3vA==",
       "dev": true,
       "dependencies": {
         "path-key": "^3.1.0",