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

CHANGELOG.md

@@ -0,0 +1,93 @@
+# Changelog
+
+All notable changes to this project are documented here.
+
+The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.1.0/),
+and this project broadly follows [Semantic Versioning](https://semver.org/spec/v2.0.0.html):
+each new wave of skills bumps the **major** version, extensions and fixes bump
+**minor** / **patch**.
+
+## [Unreleased]
+
+### Added
+- **Programmatic helpers (stdlib Python) for three flagship skills.** Each runs with
+  zero dependencies and computes part of the work instead of estimating by hand:
+  - `sprint-planning/scripts/capacity_calculator.py` — recommended sprint commitment
+    from team size, availability, velocity, and carry-over (caps at 80% of velocity).
+  - `rice-prioritisation/scripts/rice_calculator.py` — calculates and ranks RICE
+    scores from JSON/CSV and auto-flags quick wins, moonshots, and low-confidence items.
+  - `cs-health-scorecard/scripts/health_score.py` — weighted health total out of 100
+    with RAG banding and weight validation.
+- **`CHANGELOG.md`** — this file, back-filled from the release history.
+- **`SKILL-AUTHORING-STANDARD.md`** — the canonical structure every SKILL.md follows
+  (frontmatter, required sections, quality bar, anti-patterns).
+- **Skill tiers** — a `TIERS.md` reference and README section marking skills as
+  **Production-Ready**, **Stable**, or **Experimental** so new users start with the
+  strongest work.
+- **Cross-tool compatibility** — README now documents which platforms the skills work
+  on (Claude Code natively; the SKILL.md bodies port to other agents and chat LLMs).
+- **Related Projects** — README section linking to other community Claude Skills
+  libraries and the `awesome-claude-skills` / `awesome-claude-code` lists.
+
+### Changed
+- `SECURITY.md` supported-versions table updated to the current release line.
+
+## [14.0.0] — Writers & Content Creators + 7 Community Skills
+
+### Added
+- New profession **Writers & Content Creators** (`pm-writers`): Instagram Post
+  Downloader, AEO Optimizer, Thumbnail Creator, Substack Notes Scraper, Notes Humanizer.
+- `pm-cross` (+3): Sycophancy Challenger, Last 30 Days Research, NotebookLM Connector.
+- `pm-operations` (+2): Email Triage, Morning Intelligence.
+- `pm-engineering` (+2): Context Mode, Claude Superpowers.
+
+Library now spans **167 skills** across **18 professions** + 4 agent templates.
+
+## [13.0.0] — Social Media Profession
+
+### Added
+- New bundle `pm-social`: Social Media Audit, Influencer Brief, Community Management
+  Playbook, Social Ad Campaign, Viral Content Framework.
+
+## [12.0.0] — 150 Skills Milestone
+
+### Added
+- 15 skills across 10 bundles, including Cohort Analysis, Data Pipeline Spec, Renewal
+  Playbook, Customer Success Plan, 360-Degree Feedback Template, Team Health Check, Risk
+  Register, RACI Matrix, Social Media Strategy, Product Positioning Doc, Customer Journey
+  Map, User Story Writer, AI Ethics Review, Partnership Proposal, Design System Audit.
+
+Library reached **150 skills** across **16 professions**.
+
+## [11.0.0] — Engineering Expansion (500 ⭐)
+
+### Added
+- `pm-engineering` expanded to 35 skills — CI/CD, SLOs, capacity planning, DR plans,
+  threat models, schema/migration design, and more.
+
+## [10.0.0] — Customer Success + Engineering
+
+### Added
+- **Customer Success** bundle (`pm-cs`, 250 ⭐ milestone): Customer Health Scorecard,
+  QBR Deck, Escalation Brief, Churn Analysis.
+- **Engineering** (500 ⭐ milestone): CI/CD Playbook, SLO & Error Budget, Developer
+  Onboarding Doc, On-Call Runbook — plus Debugging Log Analyser, PR Description Writer,
+  System Design Interview, Changelog Generator, Test Strategy Doc, Runbook Writer.
+
+Library reached **114 skills** across **16 professions**.
+
+## [6.0.0] — 100 Skills Milestone
+
+### Added
+- Quality rebuild across all existing skills, plus 10 Figma skills.
+- 7 new skills: Teaching Lesson Plan, SEO Content Brief, Media Pitch, Change Management
+  Plan, Workshop Facilitation Guide, Sales Forecasting Model, Tax Planning Checklist.
+
+---
+
+Earlier releases (v1.0.0 – v5.0.0) predate this changelog. See the
+[article series](README.md#-the-article-series) for the full history of how the
+library grew from the first PM toolkit to 100+ skills.
+
+[Unreleased]: https://github.com/mohitagw15856/pm-claude-skills/compare/v14.0.0...HEAD
+[14.0.0]: https://github.com/mohitagw15856/pm-claude-skills/releases