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

SKILL.md

@@ -0,0 +1,116 @@
+---
+name: desktop-ctl
+description: Desktop control CLI for AI agents - screenshot, click, type, window management on Linux X11
+allowed-tools: Bash(desktop-ctl:*)
+---
+
+# desktop-ctl
+
+Desktop control CLI for AI agents on Linux X11. Provides a unified interface for screenshots, mouse/keyboard input, and window management with compact `@wN` window references.
+
+## Core Workflow
+
+1. **Snapshot** to see the desktop and get window refs
+2. **Act** using refs or coordinates (click, type, focus)
+3. **Repeat** as needed
+
+## Quick Reference
+
+### See the Desktop
+
+```bash
+desktop-ctl snapshot              # Screenshot + window tree with @wN refs
+desktop-ctl snapshot --annotate   # Screenshot with bounding boxes and labels
+desktop-ctl snapshot --json       # Structured JSON output
+desktop-ctl list-windows          # Window tree without screenshot
+desktop-ctl screenshot /tmp/s.png # Screenshot only (no window tree)
+```
+
+### Click and Type
+
+```bash
+desktop-ctl click @w1             # Click center of window @w1
+desktop-ctl click 500,300         # Click absolute coordinates
+desktop-ctl dblclick @w2          # Double-click window @w2
+desktop-ctl type "hello world"    # Type text into focused window
+desktop-ctl press enter           # Press a key
+desktop-ctl hotkey ctrl c         # Send Ctrl+C
+desktop-ctl hotkey ctrl shift t   # Send Ctrl+Shift+T
+```
+
+### Mouse Control
+
+```bash
+desktop-ctl mouse move 500 300    # Move cursor to coordinates
+desktop-ctl mouse scroll 3        # Scroll down 3 units
+desktop-ctl mouse scroll -3       # Scroll up 3 units
+desktop-ctl mouse drag 100 100 500 500  # Drag from (100,100) to (500,500)
+```
+
+### Window Management
+
+```bash
+desktop-ctl focus @w2             # Focus window by ref
+desktop-ctl focus "firefox"       # Focus window by name (substring match)
+desktop-ctl close @w3             # Close window gracefully
+desktop-ctl move-window @w1 100 200     # Move window to position
+desktop-ctl resize-window @w1 800 600   # Resize window
+```
+
+### Utilities
+
+```bash
+desktop-ctl get-screen-size       # Screen resolution
+desktop-ctl get-mouse-position    # Current cursor position
+desktop-ctl launch firefox        # Launch an application
+desktop-ctl launch code -- --new-window  # Launch with arguments
+```
+
+### Daemon
+
+```bash
+desktop-ctl daemon start          # Start daemon manually
+desktop-ctl daemon stop           # Stop daemon
+desktop-ctl daemon status         # Check daemon status
+```
+
+## Global Options
+
+- `--json` : Output as structured JSON (all commands)
+- `--session NAME` : Session name for multiple daemon instances (default: "default")
+- `--socket PATH` : Custom Unix socket path
+
+## Window Refs
+
+After `snapshot` or `list-windows`, windows are assigned short refs:
+- `@w1` is the topmost (usually focused) window
+- `@w2`, `@w3`, etc. follow z-order (front to back)
+- Refs reset on each `snapshot` call
+- Use `--json` to see stable `xcb_id` for programmatic tracking
+
+## Example Agent Workflow
+
+```bash
+# 1. See what's on screen
+desktop-ctl snapshot --annotate
+
+# 2. Focus the browser
+desktop-ctl focus "firefox"
+
+# 3. Navigate to a URL
+desktop-ctl hotkey ctrl l
+desktop-ctl type "https://example.com"
+desktop-ctl press enter
+
+# 4. Take a new snapshot to see the result
+desktop-ctl snapshot
+```
+
+## Key Names for press/hotkey
+
+Modifiers: `ctrl`, `alt`, `shift`, `super`
+Navigation: `enter`, `tab`, `escape`, `backspace`, `delete`, `space`
+Arrows: `up`, `down`, `left`, `right`
+Page: `home`, `end`, `pageup`, `pagedown`
+Function: `f1` through `f12`
+Characters: any single character (e.g. `a`, `1`, `/`)