feat: auto-detect install targets and add Gemini sync

[kieranklaassen]

Summary

• --to all / --target all — Auto-detect installed AI coding tools and install/sync to all of them in one command
• Gemini sync — sync --target gemini symlinks skills and merges MCP servers into .gemini/settings.json
• Tool detection utility — Checks config directories for OpenCode, Codex, Droid, Cursor, Pi, and Gemini

New CLI Usage

# Install to all detected tools at once
bunx @every-env/compound-plugin install compound-engineering --to all

# Sync personal config to Gemini
bunx @every-env/compound-plugin sync --target gemini

# Sync to all detected tools
bunx @every-env/compound-plugin sync --target all

Changes

• src/utils/detect-tools.ts — New utility with detectInstalledTools() and getDetectedTargetNames()
• src/sync/gemini.ts — New sync target following cursor sync pattern
• src/commands/install.ts — Added --to all handling
• src/commands/convert.ts — Added --to all handling
• src/commands/sync.ts — Added gemini + all targets, extracted syncTarget() helper

Test plan

• 8 new tests (5 detect-tools, 3 sync-gemini)
• All 139 tests passing, 0 failures
• Existing --to <target> behavior unchanged

Post-Deploy Monitoring & Validation

No additional operational monitoring required: CLI tool with no runtime service component.

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