fix: fall back to legacy API when agent create returns HTML

[michaelschecht]

Summary

• ax agents create fails because /agents/manage/create is caught by the frontend, returning HTML instead of JSON
• Added fallback: when the management API raises HTTPStatusError, retry via the legacy /api/v1/agents endpoint

Test plan

• Verified ax agents create "test-agent" --json succeeds after the fix
• Confirmed the created agent appears in ax agents list
• Verify management API path works once the backend route is fixed (fallback becomes a no-op)

🤖 Generated with Claude Code

[madtank]

Hi @michaelschecht — closing this with credit. Your fix landed on dev/staging via PR #23 (#23), which I cherry-picked from your fix/agents-create-fallback branch. The cherry-pick preserved you as the original author (Mike <michaelschecht@outlook.com>); the commit is 53827dc on dev/staging and is part of the dev/staging → main promotion PR.

Why the cherry-pick instead of merging this PR directly: your branch is based on un-formatted main, but dev/staging now has a ruff-format baseline from PR #22 that you didn't have. Re-targeting this PR's base from main to dev/staging would have produced a noisy diff fighting the format changes. Cherry-picking onto a fresh branch was the cleanest path that kept your contribution intact.

Two minor review notes I filed as future-work suggestions, not blockers (fully visible in PR #23's description):

1. The catch is httpx.HTTPStatusError which is broader than "returned HTML" — it'd also fall back on 401, 500, etc. Could narrow to specifically detect HTML responses via Content-Type / body sniff.
2. Silent fallback with no log message — adding a logger.warning("management API failed, falling back to legacy") would help debugging if the management API stays broken.

Both are nice-to-haves. The fix as-is ships real value. Thanks for the contribution!

Closing this PR — tracking further work on PR #23.