Add CLAUDE.md for AI agent context

CLAUDE.md

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+# CLAUDE.md
+
+## What is ags
+
+ags (Agents CLI) is a CLI tool to manage skills, commands, and rules across AI coding assistants (Claude Code, Cursor, Codex). It scans, lints, measures token cost, and manages everything from a single command.
+
+- Runtime: Bun (v1.0+), TypeScript, zero external dependencies
+- Entry point: `src/index.ts` (custom arg parser, dynamic command imports)
+- Package: `@moqa/ags`, v0.1.0, MIT license
+
+## Commands
+
+| Command | What it does | Key flags |
+|---------|-------------|-----------|
+| `scan` | Discover all skills/commands/agents/rules | `--agent`, `--type`, `--scope`, `--installed` |
+| `context` | What's loaded into each agent's context window | `--agent` |
+| `lint` | Validate skill files (9 rules: frontmatter, size, conflicts) | `--agent`, `--scope` |
+| `skill-cost` | Token budget per skill, context usage bars, optimization suggestions | `--scope` |
+| `grab <url>` | Install skill from GitHub URL | `--to <agent>`, `--dry-run` |
+| `rm <name>` | Remove a skill/command/agent/rule | `--agent`, `--dry-run` |
+| `stats` | Usage dashboard from Claude Code sessions | `--period` (7d/30d/90d/all-time/etc.) |
+
+All commands support `--json` (`-j`) for structured output and `--help` (`-h`).
+
+## Architecture
+
+```
+src/
+  index.ts          CLI entry, arg parsing, command routing
+  types.ts          All type definitions (AgentName, SkillType, DiscoveredSkill, etc.)
+  commands/         One file per command (scan, context, lint, budget, grab, rm, stats)
+  core/
+    agents.ts       Agent registry — paths, binaries, config files, frontmatter keys
+    scanner.ts      Discovery engine — glob-based scanning, deduplication, badge computation
+    parser.ts       YAML frontmatter parser (regex-based, not full YAML)
+    health.ts       Badge system (STALE, HEAVY, OVERSIZED, CONFLICT, SHARED)
+    tokens.ts       Token estimation (word-count heuristic: words*1.3 + symbols*0.5)
+  utils/
+    output.ts       ANSI colors, table rendering, badge/agent/scope formatting
+    github.ts       GitHub URL parsing, raw content fetching (10s timeout, 1MB limit)
+    git.ts          Git last-modified timestamp (fallback to fs mtime)
+tests/              Bun test suite (parser, tokens, health, github)
+```
+
+## Key design decisions
+
+- **Agent registry drives everything**: `src/core/agents.ts` defines paths, binaries, config files, and supported frontmatter keys per agent. All commands read from this registry — adding a new agent means adding one entry here.
+- **Deduplication by file path**: Scanner uses `Map<filePath, Skill>` so shared skills (same file, multiple agents) are not double-counted.
+- **Dynamic imports**: Commands are loaded on-demand (`import("./commands/scan.ts")`) for fast startup.
+- **Graceful fallbacks**: Missing git history, unparseable files, missing frontmatter — all handled without crashing.
+- **Streaming for large files**: Stats command streams JSONL session files line-by-line.
+
+## Supported agents
+
+| Agent | Paths scanned |
+|-------|--------------|
+| Claude Code | `~/.claude/skills/`, `.claude/skills/`, `~/.claude/commands/`, `.claude/commands/`, `~/.claude/agents/` |
+| Cursor | `.cursor/rules/**/*.mdc`, `.cursorrules` |
+| Codex | `.codex/skills/` |
+
+Context limits: Claude 200k, Cursor 120k, Codex 200k.
+
+## Adding a new agent
+
+1. Add entry to `AGENTS` in `src/core/agents.ts`
+2. Add name to `AgentName` union in `src/types.ts`
+3. Add context limit in `getContextLimit()`
+4. Add styling in `AGENT_STYLE` in `src/utils/output.ts`
+5. Update shell completions in `completions/`
+
+## Development
+
+```bash
+bun install           # install deps
+bun test              # run tests
+bun run typecheck     # type-check
+bun run dev           # run CLI directly (bun run src/index.ts)
+bun run build         # cross-platform binaries (darwin-arm64, darwin-x64, linux-x64)
+```
+
+## Lint rules
+
+The `lint` command checks for: `missing-frontmatter`, `missing-name`, `missing-description`, `short-description`, `heavy` (>5k chars), `oversized` (>500 lines), `name-conflict`, `unsupported-key`, `empty-body`. Exits with code 1 on errors.
+
+## Health badges
+
+- **STALE**: >30 days since last modification (project-scope only)
+- **HEAVY**: >5000 characters
+- **OVERSIZED**: >500 lines
+- **CONFLICT**: Same name, different file paths
+- **SHARED**: Used by multiple agents
+
+## CI
+
+GitHub Actions on push to main and PRs: install, typecheck, test (Ubuntu, Bun latest).