feat: add Cron Triggers support to module framework

- modules may declare crons: [{ schedule, name, handler }]
- handler signature (event, { db, sql, env }) matches init context
- scheduled() export in src/index.js dispatches to matching handlers with fan-out and per-handler error isolation
- registry validates cron entries and collects into registry.crons
- wrangler.toml [triggers] crons must still be populated manually by module author

src/modules/cron-dispatcher.js

@@ -0,0 +1,45 @@
+/**
+ * @file cron-dispatcher — dispatches a Cloudflare scheduled event to all
+ * matching module cron handlers.
+ *
+ * Design:
+ *  - Iterates registry.crons, filters by event.cron === entry.schedule.
+ *  - Wraps each handler invocation in try/catch so one failure cannot block
+ *    others (equivalent to Promise.allSettled fan-out via ctx.waitUntil).
+ *  - ctx.waitUntil is fire-and-forget from Workers' perspective; we wrap in
+ *    an async IIFE so errors are caught and logged rather than silently lost.
+ */
+
+import { createSqlStore } from "../db/create-sql-store.js";
+import { createStore } from "../db/create-store.js";
+
+/**
+ * @param {any} event — Cloudflare ScheduledEvent (has .cron string).
+ * @param {any} env
+ * @param {{ waitUntil: (p: Promise<any>) => void }} ctx
+ * @param {import("./registry.js").Registry} registry
+ */
+export function dispatchScheduled(event, env, ctx, registry) {
+  const matching = registry.crons.filter((entry) => entry.schedule === event.cron);
+
+  for (const entry of matching) {
+    const handlerCtx = {
+      db: createStore(entry.module.name, env),
+      sql: createSqlStore(entry.module.name, env),
+      env,
+    };
+
+    ctx.waitUntil(
+      (async () => {
+        try {
+          await entry.handler(event, handlerCtx);
+        } catch (err) {
+          console.error(
+            `[cron] handler "${entry.name}" (module "${entry.module.name}", schedule "${entry.schedule}") failed:`,
+            err,
+          );
+        }
+      })(),
+    );
+  }
+}