feat(agent): implement content generation agent for bounty outcomes (#5)

[angelTomo9]

Summary

Resolves #5 by implementing the Content-Generation Agent to synthesize social media announcements, Twitter threads, and blog articles from bounty completions.

Acceptance Criteria Checklist

• Core Function: generateContent(bounty) returns { tweet, thread, blogPost }.
• Multi-format Generation: Single 280-char tweet, 5-tweet viral thread, 300-word case study blog post.
• Unit Tests: Full verification with mock bounty payload in ests/content-agent.test.ts.

Wallet: 0x9f8F72aA9304c8B593d555F12eF6589cC3A579A2

Closes #5