Add cross-tool positioning, Python helpers, tiers, and hygiene docs

Five improvements to position the library as a serious engineering project:

1. Cross-tool compatibility — new README "Works With" section honestly
   documenting where skills run (Claude Code natively; SKILL.md bodies
   port to other agents and chat LLMs as system prompts).

2. Python helper scripts (stdlib-only) for the three strongest skills:
   - sprint-planning: capacity_calculator.py (recommended commitment)
   - rice-prioritisation: rice_calculator.py (ranks, flags quick wins/moonshots)
   - cs-health-scorecard: health_score.py (weighted total + RAG)
   Each is wired into its SKILL.md and synced to the plugin copies.

3. Explicit skill tiering — TIERS.md + README section marking 46
   Production-Ready skills and calling out Experimental (external-dependency)
   ones; everything else is Stable.

4. Repository hygiene — new CHANGELOG.md (Keep a Changelog format) and
   SKILL-AUTHORING-STANDARD.md; refreshed SECURITY.md version table and
   helper-script disclosure; added .gitignore.

5. Related Projects — README section linking to alirezarezvani/claude-skills
   and the major awesome-claude-skills / awesome-claude-code lists.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_016JWn5jRD5tcEFKrubjQ6Px

scripts/setup-marketplace.sh

@@ -55,6 +55,7 @@ cp skills/feature-prioritisation/SKILL.md    plugins/pm-planning/skills/feature-
 cp skills/roadmap-presentation/SKILL.md      plugins/pm-planning/skills/roadmap-presentation/SKILL.md
 cp skills/pricing-strategy/SKILL.md          plugins/pm-planning/skills/pricing-strategy/SKILL.md
 cp skills/rice-prioritisation/SKILL.md       plugins/pm-planning/skills/rice-prioritisation/SKILL.md
+cp -r skills/rice-prioritisation/scripts     plugins/pm-planning/skills/rice-prioritisation/ 2>/dev/null || true
 cp skills/roadmap-narrative/SKILL.md         plugins/pm-planning/skills/roadmap-narrative/SKILL.md
 cp skills/rice-impact-matrix/SKILL.md        plugins/pm-planning/skills/rice-impact-matrix/SKILL.md
 
@@ -73,6 +74,7 @@ mkdir -p plugins/pm-delivery/skills/sprint-brief
 mkdir -p plugins/pm-delivery/skills/retro-analysis
 
 cp skills/sprint-planning/SKILL.md           plugins/pm-delivery/skills/sprint-planning/SKILL.md
+cp -r skills/sprint-planning/scripts         plugins/pm-delivery/skills/sprint-planning/ 2>/dev/null || true
 cp skills/technical-spec-template/SKILL.md   plugins/pm-delivery/skills/technical-spec-template/SKILL.md
 cp skills/ab-test-planner/SKILL.md           plugins/pm-delivery/skills/ab-test-planner/SKILL.md
 cp skills/go-to-market-planner/SKILL.md      plugins/pm-delivery/skills/go-to-market-planner/SKILL.md