Migrate to Docker: containerize for docker-server deployment

- Add Dockerfile + cron.js (daily 4pm UTC loop replacing EC2 cron)
- Add infra/docker-compose.yml and deploy-stack.sh for Portainer
- Support DATA_DIR env var in bot.js for persistent history volume
- Support PROMPTS_JSON env var in cron.js (no SSH needed for config)

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

cron.js

@@ -0,0 +1,49 @@
+import { execFileSync } from "child_process";
+import { writeFileSync } from "fs";
+import { fileURLToPath } from "url";
+import { dirname, join } from "path";
+
+const __dirname = dirname(fileURLToPath(import.meta.url));
+
+const PROMPT_NAME = process.env.PROMPT_NAME;
+if (!PROMPT_NAME) {
+  console.error("PROMPT_NAME env var required");
+  process.exit(1);
+}
+
+// Write prompts.json from env var.
+// Future: if PROMPTS_URL is set, fetch from S3 or similar instead.
+if (process.env.PROMPTS_JSON) {
+  writeFileSync(join(__dirname, "prompts.json"), process.env.PROMPTS_JSON);
+  console.log(`[${PROMPT_NAME}] Wrote prompts.json from PROMPTS_JSON env var`);
+} else {
+  console.error("PROMPTS_JSON env var required");
+  process.exit(1);
+}
+
+function msUntilNext4pmUTC() {
+  const now = new Date();
+  const next = new Date(now);
+  next.setUTCHours(16, 0, 0, 0);
+  if (next <= now) next.setUTCDate(next.getUTCDate() + 1);
+  return next - now;
+}
+
+function runScheduler() {
+  console.log(`[${PROMPT_NAME}] Running scheduler at ${new Date().toISOString()}`);
+  try {
+    execFileSync("node", [join(__dirname, "scheduler.js"), PROMPT_NAME], { stdio: "inherit" });
+  } catch {
+    console.error(`[${PROMPT_NAME}] scheduler.js exited with error`);
+  }
+  scheduleNext();
+}
+
+function scheduleNext() {
+  const ms = msUntilNext4pmUTC();
+  const next = new Date(Date.now() + ms);
+  console.log(`[${PROMPT_NAME}] Next run at ${next.toISOString()}`);
+  setTimeout(runScheduler, ms);
+}
+
+scheduleNext();