improvement(providers): tighten Gemini and vLLM agent-attachment ceilings (#5095)

A live-doc audit of the merged large-file feature found two ceilings that were
higher than the provider actually accepts:
- Gemini: 100MB -> 50MB. Gemini hard-caps PDFs at 50MB, so a 50-100MB PDF passed
  our gate, got uploaded + polled, then failed at generateContent. 50MB respects
  the documented limit and is more memory-safe.
- vLLM: 50MB -> 25MB. vLLM's default image-fetch timeout is 5s; a 50MB remote
  fetch routinely exceeds it. 25MB aligns with that reality and matches Baseten
  (the other vLLM-backed provider).

apps/sim/providers/models.ts

@@ -195,7 +195,7 @@ export const PROVIDER_DEFINITIONS: Record<string, ProviderDefinition> = {
   },
   vllm: {
     id: 'vllm',
-    fileAttachment: { maxBytes: 50 * 1024 * 1024, strategy: 'remote-url' },
+    fileAttachment: { maxBytes: 25 * 1024 * 1024, strategy: 'remote-url' },
     name: 'vLLM',
     icon: VllmIcon,
     description: 'Self-hosted vLLM with an OpenAI-compatible API',
@@ -1319,7 +1319,7 @@ export const PROVIDER_DEFINITIONS: Record<string, ProviderDefinition> = {
   },
   google: {
     id: 'google',
-    fileAttachment: { maxBytes: 100 * 1024 * 1024, strategy: 'files-api' },
+    fileAttachment: { maxBytes: 50 * 1024 * 1024, strategy: 'files-api' },
     name: 'Google',
     description: "Google's Gemini models",
     defaultModel: 'gemini-2.5-pro',