Prepare for public repo: gitignore prompts.json, add examples

- prompts.json now gitignored (contains account-specific config)
- Added prompts.example.json showing config structure
- Added .env.example with credential template

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

prompts.example.json

@@ -0,0 +1,35 @@
+[
+  {
+    "name": "example-promo",
+    "account": "myaccount",
+    "prompt": "Write a casual tweet that makes someone curious enough to click the link. No hashtags. Keep it under 280 characters. Just the tweet, nothing else.\n\nEnd the tweet with <link> on its own line.",
+    "links": {
+      "link": "https://example.com"
+    },
+    "schedule": {
+      "type": "random",
+      "window": [
+        8,
+        20
+      ],
+      "minDays": 2
+    }
+  },
+  {
+    "name": "example-daily",
+    "account": "myaccount",
+    "prompt": "Write a witty tweet about coffee. No hashtags. Generate 1 tweet. Just the tweet, nothing else.",
+    "schedule": {
+      "type": "daily",
+      "window": [
+        8,
+        20
+      ],
+      "postsPerDay": [
+        1,
+        3
+      ],
+      "minGapHours": 4
+    }
+  }
+]