What type of PR is this?

/kind feature

What this PR does / why we need it:

Adds the first version of Grove scale-test CI history tracking.

This PR adds:

• operator/hack/scale-history.py for storing scale-test results in a history branch.
• A compact index/metrics.ndjson metric index plus raw scale-test-results.json storage.
• A minimal static dashboard under operator/hack/scale-dashboard/.
• A scheduled/manual GitHub Actions workflow that runs the scale test and stores successful results.
• README docs for local ingestion and dashboard validation.

The workflow disables routine profiling/pprof collection, compiles the scale test before creating the KWOK cluster, and uploads short-retention diagnostics on failure.

Which issue(s) this PR fixes:

Fixes #550

Special notes for your reviewer:

The workflow is intentionally manual/scheduled only for v1. It does not run on PR labels.

The history branch is expected to be public and served by GitHub Pages. Routine runs store only timing history and raw scale-test JSON, not profiling artifacts.

Validation done:

• Parsed workflow YAML.
• Ran git diff --check.
• Verified scale-history.py --help.
• Ran scale-history.py local on a sample result and confirmed duplicate ingestion is skipped.

Does this PR introduce a API change?

NONE

Additional documentation e.g., enhancement proposals, usage docs, etc.:

operator/hack/README.md documents scale-history.py local/branch usage and local dashboard validation.