diagnose: support memory_limiter percentages

[sb123sb123]

Closes #24.

Teach diagnose to recognize OpenTelemetry Collector's limit_percentage and spike_limit_percentage settings for memory_limiter. The static checks enforce the pinned Collector v0.161.0 rules: at least one nonzero limit, percentage values in the accepted range, and each configured spike limit below its matching limit. A nonzero limit_mib retains precedence, while configured percentage fields are still validated.

The report continues to identify invalid fields by YAML path and line without including their values. Unknown settings remain indeterminate. The documentation states that this is a static configuration check and does not assess host memory sufficiency.

Validation on remote Windows via WSL Ubuntu 22.04 with Go 1.26.8:

• go test ./internal/diagnose ./internal/cli -count=1
• go vet ./...
• gofmt check and git diff --check

[kwisatzh]

thanks! will review this week.