Post-Merge Docs/Test Review workflows: invalid model + daily-limit overrun

[JacobPEvans]

Symptom

In `tf-splunk-aws` (and likely all consumers of the shared post-merge review workflows):

• Post-Merge Docs Review: 33 failures / 100 runs
• Post-Merge Test Review: 20 failures / 100 runs

Root cause — two distinct issues

1. Invalid model alias

`anthropics/claude-code-action@v1` configured with `model: openrouter/free`. The action rejects it:

```text
There's an issue with the selected model (openrouter/free).
It may not exist or you may not have access to it.
```

`openrouter/free` is not a valid OpenRouter model slug.

2. Daily-limit overrun (Test Review)

Hits `Daily limit reached (5/5 runs in last 24h)` guard — the workflow fires more than 5x/day on every `main` push.

Fix (in shared workflow at `JacobPEvans/.github`)

1. Replace model: `openrouter/free` → a valid slug. Options:
   • `claude-sonnet-4-5` (default Claude)
   • `openrouter/anthropic/claude-3.5-sonnet` (real OpenRouter path)
   • `gemini/gemini-3-pro-preview` if routing through Bifrost
2. Restrict triggers: only fire on actual PR merges (not every main commit), OR raise the daily-limit gate to match expected merge volume.

Affected files

• `.github/workflows/post-merge-docs-review.yml` (this repo)
• `.github/workflows/post-merge-test-review.yml` (this repo)
• Per-repo callers inherit the fix