feat: add Gemini CLI + OpenClaw support, fix Codex missing 25 skills

Gemini CLI:
- Add GEMINI.md with activation instructions
- Add scripts/gemini-install.sh setup script
- Add scripts/sync-gemini-skills.py (194 skills indexed)
- Add .gemini/skills/ with symlinks for all skills, agents, commands
- Remove phantom medium-content-pro entries from sync script
- Add top-level folder filter to prevent gitignored dirs from leaking

Codex CLI:
- Fix sync-codex-skills.py missing "engineering" domain (25 POWERFUL skills)
- Regenerate .codex/skills-index.json: 124 → 149 skills
- Add 25 new symlinks in .codex/skills/

OpenClaw:
- Add OpenClaw installation section to INSTALLATION.md
- Add ClawHub install + manual install + YAML frontmatter docs

Documentation:
- Update INSTALLATION.md with all 4 platforms + accurate counts
- Update README.md: "three platforms" → "four platforms" + Gemini quick start
- Update CLAUDE.md with Gemini CLI support in v2.1.1 highlights
- Update SKILL-AUTHORING-STANDARD.md + SKILL_PIPELINE.md with Gemini steps
- Add OpenClaw + Gemini to installation locations reference table

Marketplace: all 18 plugins validated — sources exist, SKILL.md present

Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>

GEMINI.md

@@ -0,0 +1,67 @@
+# Gemini CLI Foundations
+
+This repository is a **comprehensive skills library** for Gemini CLI - reusable, production-ready skill packages that bundle domain expertise, best practices, analysis tools, and strategic frameworks.
+
+## Using Skills with Gemini CLI
+
+Gemini CLI can activate any skill in this repository using the `activate_skill` tool.
+
+### Skill Locations
+
+Skills are organized into domain folders. Each skill is a directory containing a `SKILL.md` file.
+
+| Domain | Folder |
+|--------|--------|
+| **Engineering (Core)** | `engineering-team/` |
+| **Engineering (Advanced)** | `engineering/` |
+| **Product Team** | `product-team/` |
+| **Marketing Skills** | `marketing-skill/` |
+| **C-Level Advisory** | `c-level-advisor/` |
+| **Project Management** | `project-management/` |
+| **Regulatory & QM** | `ra-qm-team/` |
+| **Business & Growth** | `business-growth/` |
+| **Finance** | `finance/` |
+
+### Activating a Skill
+
+To activate a skill, use the folder name. For example:
+
+```javascript
+activate_skill(name="senior-architect")
+activate_skill(name="content-creator")
+activate_skill(name="cto-advisor")
+```
+
+The Gemini CLI will search for the corresponding `SKILL.md` file within the repository and load its instructions.
+
+## Agents & Commands
+
+In addition to skills, this repository provides specialized **Agents** and **Commands**.
+
+- **Agents** (`agents/`): Multi-agent personas for complex coordination (e.g., `cs-engineering-lead`).
+- **Commands** (`commands/`): Predefined workflows for common tasks (e.g., `/tdd`, `/tech-debt`).
+
+Activate them as skills:
+```javascript
+activate_skill(name="cs-engineering-lead")
+activate_skill(name="tdd")
+```
+
+## Python Automation Tools
+
+Each skill includes deterministic Python CLI tools in its `scripts/` folder. These use the standard library only.
+
+Example usage:
+```bash
+python3 marketing-skill/content-production/scripts/seo_checker.py article.txt
+```
+
+## Setup for Gemini CLI Users
+
+Run the setup script to initialize the Gemini-specific skill index and symlinks:
+
+```bash
+./scripts/gemini-install.sh
+```
+
+This will create a `.gemini/skills/` directory for easier discovery.