Phase 6: utility commands, SKILL.md, AGENTS.md, README.md

- Implement screen_size via xcap Monitor, mouse_position via x11rb
  query_pointer, standalone screenshot with optional annotation,
  launch for spawning detached processes
- Handler dispatchers for get-screen-size, get-mouse-position,
  screenshot, launch
- SKILL.md agent discovery file with allowed-tools frontmatter
- AGENTS.md contributor guidelines for AI agents
- README.md with installation, quick start, architecture overview

AGENTS.md

@@ -0,0 +1,40 @@
+# Agent Guidelines
+
+## Build
+
+```bash
+cargo build
+cargo clippy
+```
+
+## Run
+
+Requires an X11 session with `DISPLAY` set.
+
+```bash
+cargo run -- snapshot
+cargo run -- --json snapshot --annotate
+```
+
+## Code Style
+
+- No emojis in code or comments
+- Use `anyhow::Result` for all fallible functions
+- All daemon handler functions are async
+- Match field naming between CLI args, NDJSON protocol, and JSON output
+
+## Architecture
+
+- `src/cli/` - clap CLI parser and client-side socket connection
+- `src/daemon/` - tokio async daemon, request handler, state management
+- `src/backend/` - DesktopBackend trait and X11 implementation
+- `src/core/` - shared types, protocol, ref map, session detection
+
+## Adding a New Command
+
+1. Add the variant to `Command` enum in `src/cli/mod.rs`
+2. Add request building in `build_request()` in `src/cli/mod.rs`
+3. Add the action handler in `src/daemon/handler.rs`
+4. Add the backend method to `DesktopBackend` trait in `src/backend/mod.rs`
+5. Implement in `src/backend/x11.rs`
+6. Update `SKILL.md`