refactor: move TLE text parsing into a portable source module

The satellites layer parsed catalog text inside its Cesium-backed orbit
owner. Move the parser unchanged to src/sources/tle.js, add a catalog
number helper, and have the layer delegate to it so code outside the
layer can read TLE text without loading rendering.

src/sources/tle.js

@@ -0,0 +1,27 @@
+/**
+ * Parse three-line TLE catalog text into `{ name, line1, line2 }` entries.
+ * Blocks whose second and third lines are not TLE lines 1 and 2 are skipped.
+ */
+export function parseTleText(text) {
+  const lines = String(text)
+    .trim()
+    .split('\n')
+    .map((line) => line.trim())
+    .filter((line) => line.length > 0);
+  const result = [];
+  for (let i = 0; i < lines.length - 2; i += 3) {
+    const name = lines[i];
+    const line1 = lines[i + 1];
+    const line2 = lines[i + 2];
+    if (line1.startsWith('1 ') && line2.startsWith('2 ')) {
+      result.push({ name, line1, line2 });
+    }
+  }
+  return result;
+}
+
+/** The NORAD catalog number from TLE line 1, or null. */
+export function tleCatalogNumber(line1) {
+  const number = Number.parseInt(String(line1).slice(2, 7), 10);
+  return Number.isInteger(number) ? number : null;
+}