Revert claude-review to single-step + add Anthropic API key preflight

[TimJohns]

Two changes, both following from the July 2026 debugging incident where the claude-review failures turned out to be the Anthropic API rejecting the key ($0 cost / is_error), not a workflow-config problem.

1. Revert PR #12 / #13 back to the single-step config

Restores the claude-review job to its pre-#12 form: one claude-code-action call (track_progress for the rich comment + --json-schema for the gate). The two-step rebuild was chasing a misdiagnosis and doubled the Claude cost for no benefit.

2. Add an Anthropic key preflight (the detection mechanism)

Before the costly review runs, a minimal 1-token Anthropic call checks that the key/account can actually make requests:

• 200 → proceed.
• 401 → posts a PR comment: the ANTHROPIC_API_KEY is invalid/revoked — rotate it.
• 400 / 402 → posts a PR comment: the account likely has no credit / a billing issue — check the balance & billing at the Anthropic Console — and fails fast.
• 429 / network / other → warn and let the review run (don't block on transients).

This replaces the opaque did not return structured_output failure with a clear, actionable message pointing at the real cause.

Note: this restores track_progress + --json-schema in one call. Whether that combination reliably yields both a comment and structured output was never actually validated (every prior run failed on the key first). Once the Anthropic account is healthy, the preflight passes and we can confirm the review works end-to-end — and revisit the config then if needed.

🤖 Generated with Claude Code