chore: add ESLint with eslint-plugin-jsdoc and central typedefs

- flat config, JSDoc-only rules (no stylistic — Biome owns those)
- src/types.js defines Env, Module, Command, Cron, ModuleContext, Trade
- lint script now runs biome check + eslint src

eslint.config.js

@@ -0,0 +1,57 @@
+import jsdoc from "eslint-plugin-jsdoc";
+
+// Cloudflare Workers globals + custom codebase types that no-undefined-types
+// must treat as defined (no tsc/jsconfig — plain ESM JS).
+const DEFINED_TYPES = [
+  // Cloudflare Workers runtime globals
+  "KVNamespace",
+  "D1Database",
+  "D1PreparedStatement",
+  // Web globals not always in eslint's scope
+  "Request",
+  "Response",
+  "URL",
+  // KV interface types (src/db/kv-store-interface.js)
+  "KVStore",
+  "KVStorePutOptions",
+  "KVStoreListOptions",
+  "KVStoreListResult",
+  // SQL interface types (src/db/sql-store-interface.js)
+  "SqlStore",
+  "SqlRunResult",
+  // Central typedefs (src/types.js)
+  "Env",
+  "Module",
+  "Command",
+  "Cron",
+  "ModuleContext",
+  "Trade",
+  "Portfolio",
+  "PortfolioMeta",
+  // Module sub-types (registry, validate-*)
+  "BotModule",
+  "RegistryEntry",
+  "Registry",
+  "ModuleCommand",
+  "ModuleCron",
+  "CronEntry",
+  // Trading sub-types
+  "ResolvedSymbol",
+];
+
+export default [
+  {
+    files: ["src/**/*.js"],
+    plugins: { jsdoc },
+    rules: {
+      "jsdoc/check-alignment": "warn",
+      "jsdoc/check-param-names": "error",
+      "jsdoc/check-tag-names": "error",
+      "jsdoc/check-types": "error",
+      "jsdoc/no-undefined-types": ["error", { definedTypes: DEFINED_TYPES }],
+      "jsdoc/require-param-type": "error",
+      "jsdoc/require-returns-type": "error",
+      "jsdoc/valid-types": "error",
+    },
+  },
+];