docs(agent): streamline guidance and skills

Keep always-on instructions concise and route specialized work through focused skills. Split large skills into progressive references and add dedicated change, desktop, sync, and performance guidance.

.agents/skills/clack-cli-patterns/references/snippets.md

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+# CLI Output Snippets
+
+## Prompt Guard
+
+```js
+if (canPrompt(options)) {
+  const value = await select({
+    message: 'Choose an option',
+    options: [{ value: 'a', label: 'Option A' }],
+  });
+  if (isCancel(value)) {
+    cancel('Operation cancelled.');
+    return;
+  }
+}
+```
+
+## Non-Interactive Fallback
+
+```js
+if (!resolvedValue) {
+  if (canPrompt(options)) {
+    // prompt path
+  } else {
+    throw new Error('Missing required value. Provide --flag <value>.');
+  }
+}
+```
+
+## Spinner Guard
+
+```js
+const spin = createSpinner(options);
+spin?.start('Running operation...');
+// ...work...
+spin?.stop('Done');
+```
+
+## JSON vs Human Output
+
+```js
+if (options.json) {
+  printJson({ ok: true, data });
+  return;
+}
+
+intro('Operation');
+log.success('Completed');
+outro('done');
+```