fix: bump agno 2.5.17 + add Doc Writer agent

[Mustafa-Esoofally]

Summary

• Bumps agno from 2.5.14 to 2.5.17
• Fixes IndexError: list index out of range in get_pull_requests when a repo has fewer PRs than the requested limit (Fix IndexError in get_pull_requests when fewer PRs than requested limit agno#7353)
• Adds Doc Writer agent — writes and improves documentation by cross-referencing SDK source code against the docs repo

Doc Writer Agent

• Reads SDK source to understand features, checks existing docs for gaps
• Writes .mdx docs following Diataxis framework (tutorials, how-tos, reference, explanation)
• Creates PRs on the docs repo via worktrees
• Cross-references SDK code, cookbooks, and existing docs for accuracy

Test Results (local, agno 2.5.17)

• get_pull_requests — no IndexError on repos with few PRs
• get_pull_request, get_pull_request_changes — working
• list_issues, list_branches — working
• Full team loads (6 members) with Doc Writer

Test Plan

• Deploy to Railway
• Test Doc Writer via Slack: "@coda what docs are missing for feature X?"
• Verify Explorer get_pull_requests no longer errors in logs