Feat: Implement version sync and iterate to 0.3.21

- Added a version sync orchestrator script to ensure consistent versioning across project files.
- Configured `deno task build` to automatically synchronize versions before compiling.
- Set the project version to 0.3.21 in `deno.json` and propagated it throughout the codebase.

scripts/sync-version.ts

@@ -0,0 +1,45 @@
+// scripts/sync-version.ts
+const denoConfig = JSON.parse(await Deno.readTextFile("deno.json"));
+const version = denoConfig.version;
+
+console.log(`Syncing version ${version} across project files...`);
+
+const filesToUpdate = [
+  {
+    path: "icalendar.ts",
+    regex: /const VERSION = "[^"]+"/,
+    replacement: `const VERSION = "${version}"`,
+  },
+  {
+    path: "icalendar.plug.yaml",
+    regex: /^version: .*/m,
+    replacement: `version: ${version}`,
+  },
+  {
+    path: "PLUG.md",
+    regex: /version: .*/, 
+    replacement: `version: "${version}"`,
+  },
+];
+
+for (const file of filesToUpdate) {
+  try {
+    let content = await Deno.readTextFile(file.path);
+    if (!content.match(file.regex)) {
+        // If PLUG.md doesn't have version:, add it after the name: line
+        if (file.path === "PLUG.md") {
+            content = content.replace(/^name: .*/m, (match) => `${match}
+version: "${version}"`);
+        } else {
+            console.warn(`⚠️ Could not find regex in ${file.path}, skipping.`);
+            continue;
+        }
+    } else {
+        content = content.replace(file.regex, file.replacement);
+    }
+    await Deno.writeTextFile(file.path, content);
+    console.log(`✅ Updated ${file.path}`);
+  } catch (e) {
+    console.error(`❌ Could not update ${file.path}: ${e.message}`);
+  }
+}