fix: treat screenshot failure as non-critical in browser tool

[atian8179]

Problem

In backend/pkg/tools/browser.go, the ContentMD, ContentHTML, and Links methods run two concurrent operations: fetching page content and capturing a screenshot. If the screenshot fails (scraper unavailable, timeout, image too small), the function returns an error discarding successfully-fetched page content.

The AI agent receives an error instead of the content it needs. Screenshot is a non-critical side-effect — PutScreenshot already ignores errors at the call-site.

Reported in #149.

Solution

Log a warning on screenshot failure instead of returning an error. Content is preserved.

if errScreenshot != nil {
    log.Printf("Warning: screenshot failed for %s (content still available): %v", url, errScreenshot)
    screenshotName = ""
}

Changes

• backend/pkg/tools/browser.go: 3 methods changed — ContentMD(), ContentHTML(), Links() (+6/-3)

Testing

• Content succeeds + screenshot fails → content returned ✅
• Both succeed → unchanged ✅
• Content fails → error returned ✅

Closes #149

[asdek]

thank you for the PR, but these changes were included by #150