Improve content-renderer warnings to include post/author context

Problem

The content-renderer logs warnings when blocking content, but doesn't include context about which post triggered the warning:

[@hiveio/content-renderer]. | 2025-12-10T23:01:51.676Z [warn]: Blocked, image tag src does not appear to be a url; img
[@hiveio/content-renderer]. | 2025-12-10T23:07:08.014Z [warn]: Blocked, did not match iframe "src" white list urls:; iframe

This makes it impossible to:

• Debug which posts have broken content
• Identify patterns in blocked content
• Help users fix their posts
• Verify if legitimate content is being incorrectly blocked

Desired Output

[@hiveio/content-renderer]. | [warn]: Blocked image (invalid src) in @author/permlink: src="img"
[@hiveio/content-renderer]. | [warn]: Blocked iframe (not whitelisted) in @author/permlink: src="https://example.com/embed"

Tasks

• Investigate how content-renderer is called in Denser
• Add post context (author/permlink) to renderer calls
• Update warning messages to include context
• Review iframe whitelist configuration
• Consider if whitelist needs updates

Related

• @hiveio/content-renderer package
• Content sanitization/security