fix: harden deploys and close top security holes after /events outage

Isolate next dev from production .next, add build-guard/atomic deploy/health
watchdog, error boundaries, and fix JWT startup, meetup leaks, media path
traversal, SVG/memory uploads, and JSON-LD escaping.

Co-authored-by: Cursor <cursoragent@cursor.com>

frontend/tsconfig.json

@@ -16,6 +16,13 @@
     "plugins": [{ "name": "next" }],
     "paths": { "@/*": ["./*"] }
   },
-  "include": ["next-env.d.ts", "**/*.ts", "**/*.tsx", ".next/types/**/*.ts"],
+  "include": [
+    "next-env.d.ts",
+    "**/*.ts",
+    "**/*.tsx",
+    ".next/types/**/*.ts",
+    ".next-dev/types/**/*.ts",
+    ".next-build/types/**/*.ts"
+  ],
   "exclude": ["node_modules"]
 }