Feature: Add SDK Reference Cron Job

[ben-fornefeld]

Note

Medium Risk
Medium risk because it changes the docs automation workflow behavior and permissions (adds scheduled runs and PR creation), which could increase run frequency and affect repo write operations if misconfigured.

Overview
Adds a 15-minute scheduled trigger to the SDK reference sync workflow, with default parameters (sdk=all, version=all, limit=3) to act as a polling fallback.

Changes the workflow to stop pushing directly to main; it now detects whether docs/sdk-reference/** or docs.json changed and, if so, uses peter-evans/create-pull-request to create/update an automation PR with run/trigger metadata and a richer step summary.

Expands the generator test workflow’s pull_request path filters to include the sync workflow and generated-doc inputs, and updates sdk-reference-generator/README.md to document the scheduled sync and PR-based output behavior.

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