ci: classify packages/**/*.md-only diffs as docs-only + harness guidance to apply ci:skip labels on doc PRs

[rickylabs]

From pilot eval I8 (owner note during beta.6 wrap-up). The docs-only skip policy in .github/scripts/ci-classify-changes.ts requires the diff to never touch packages//plugins/ — so a README-only pass like PR #610 (10 markdown files, zero source) still ran the full scaffold-static + scaffold-runtime (aspire/docker/postgres) gates.

Acceptance

• Classifier treats a diff whose every changed path matches **/*.md(x) as docs-only regardless of directory (rename-aware rule preserved; deno.json*, deno.lock, workflows still force full). Evidence: PR fix(ci): classify *.md-only diffs as docs-only + skill guidance for ci:skip labels (#611) #613 slice 2, commit 34b33781, and its 30/30 classifier-test phase comment.
• netscript-harness / netscript-pr skill guidance: when opening a doc-only PR, apply ci:skip-e2e (+ ci:skip-scaffold when applicable) proactively; ci:full remains the escape hatch. Evidence: PR fix(ci): classify *.md-only diffs as docs-only + skill guidance for ci:skip labels (#611) #613 slice 3, commit 9279e40c, and its mirror-check phase comment.

Parent: #601. Refs #610 (the motivating PR). Filed by beta6-ship orchestrator fb43bc3e.