WIP: Gemini CLI extension infrastructure

Add experimental Gemini CLI extension with MCP server that exposes
skills as individual tools. Infrastructure works but auto-triggering
skills is blocked by Gemini CLI treating context files as advisory
rather than executable instructions.

See issue #128 for detailed findings.

- gemini-extension.json manifest
- MCP server with individual skill tools
- GEMINI.md bootstrap attempts (don't work)
- Installation documentation

.gemini/INSTALL.md

@@ -0,0 +1,159 @@
+# Installing Superpowers for Gemini CLI
+
+## Prerequisites
+
+- [Gemini CLI](https://github.com/google-gemini/gemini-cli) installed
+- Node.js installed
+- Git installed
+
+## Installation Steps
+
+### 1. Install from GitHub
+
+```bash
+gemini extensions install https://github.com/obra/superpowers
+```
+
+Or install from a local clone:
+
+```bash
+git clone https://github.com/obra/superpowers.git ~/.config/gemini/superpowers
+gemini extensions link ~/.config/gemini/superpowers/.gemini
+```
+
+### 2. Build the MCP Server
+
+If installing from local:
+
+```bash
+cd ~/.gemini/extensions/superpowers/mcp-server
+npm install
+npm run build
+```
+
+### 3. Restart Gemini CLI
+
+Restart Gemini CLI. The extension will automatically load the superpowers context.
+
+You should see superpowers is active when you ask "do you have superpowers?"
+
+## Usage
+
+### Finding Skills
+
+Use the `find_skills` tool to list all available skills:
+
+```
+use find_skills tool
+```
+
+### Loading a Skill
+
+Use the `use_skill` tool to load a specific skill:
+
+```
+use use_skill tool with skill_name: "superpowers:brainstorming"
+```
+
+### Personal Skills
+
+Create your own skills in `~/.config/gemini/skills/`:
+
+```bash
+mkdir -p ~/.config/gemini/skills/my-skill
+```
+
+Create `~/.config/gemini/skills/my-skill/SKILL.md`:
+
+```markdown
+---
+name: my-skill
+description: Use when [condition] - [what it does]
+---
+
+# My Skill
+
+[Your skill content here]
+```
+
+Personal skills override superpowers skills with the same name.
+
+### Project Skills
+
+Create project-specific skills in your project:
+
+```bash
+# In your project directory
+mkdir -p .gemini/skills/my-project-skill
+```
+
+Create `.gemini/skills/my-project-skill/SKILL.md`:
+
+```markdown
+---
+name: my-project-skill
+description: Use when [condition] - [what it does]
+---
+
+# My Project Skill
+
+[Your skill content here]
+```
+
+**Skill Priority:** Project skills override personal skills, which override superpowers skills.
+
+**Skill Naming:**
+- `project:skill-name` - Force project skill lookup
+- `skill-name` - Searches project → personal → superpowers
+- `superpowers:skill-name` - Force superpowers skill lookup
+
+## Tool Mapping
+
+When skills reference tools from other environments:
+
+| Skill References | Gemini CLI Equivalent |
+|------------------|----------------------|
+| `TodoWrite` | `write_todos` |
+| `Skill` tool | `use_skill` |
+| `Read`, `Write`, `Edit` | Your native file tools |
+| `Bash` | `run_shell_command` |
+| `Task` with subagents | Break into sequential steps |
+
+## Updating
+
+```bash
+gemini extensions update superpowers
+```
+
+Or if installed locally:
+
+```bash
+cd ~/.config/gemini/superpowers
+git pull
+cd .gemini/mcp-server
+npm run build
+```
+
+## Troubleshooting
+
+### Extension not loading
+
+1. Check extension is installed: `gemini extensions list`
+2. Verify MCP server is built: `ls ~/.gemini/extensions/superpowers/mcp-server/dist/`
+3. Check Gemini CLI logs for errors
+
+### Skills not found
+
+1. Verify skills directory exists: `ls ~/.gemini/extensions/superpowers/skills`
+2. Use `find_skills` tool to see what's discovered
+3. Check file structure: each skill should have a `SKILL.md` file
+
+### MCP Server errors
+
+1. Rebuild: `cd ~/.gemini/extensions/superpowers/mcp-server && npm run build`
+2. Check Node.js version: `node --version` (requires Node 18+)
+
+## Getting Help
+
+- Report issues: https://github.com/obra/superpowers/issues
+- Documentation: https://github.com/obra/superpowers