feat: Add previous comments to issue context for better conversation awareness

[roger704]

Summary

This PR improves conversation context by fetching previous comments and always including the issue description, not just on the first message.

Problem

On follow-up comments to an issue, the agent only received the new comment text with no context of:

• The original issue description (only included for the first message)
• Previous comments in the thread
• What it had said or done before

This led to:

• Repetitive responses (agent doesn't know what it already said)
• Contradictory suggestions (forgets previous recommendations)
• Loss of context in multi-turn conversations

Solution

1. Fetch Previous Comments

New fetchIssueComments() method retrieves up to 10 recent relevant comments:

const { data: comments } = await this.octokit.rest.issues.listComments({
  owner, repo, issue_number: issueNumber, per_page: 20
});

Bot acknowledgments are filtered out to keep context relevant.

2. Always Include Issue Context

Changed from:

if (isNewConversation) {
  finalMessage = this.buildIssueContext(issue, strippedComment);
}

To:

// Always include context, not just for new conversations
finalMessage = await this.buildIssueContext(owner, repo, issue, strippedComment);

3. Enhanced Context Format

The context now includes:

[GitHub Issue Context]
Issue #123: "Bug in login flow"
Author: user
Labels: bug
Status: open

Description:
<original issue body>

Previous Comments:
**user**: First comment...
**bot**: Response...
**user**: Follow-up...

---

<current user comment>

Benefits

• Full conversation history - Agent sees what was discussed before
• Continuity - Can continue work from where it left off
• No repetition - Knows what it already said
• Better follow-ups - Understands context of user's questions

Testing

Tested in production with multi-turn conversations - agent now correctly references previous discussion and avoids repetition.