refactor: enforce device labels, unify screenshot, remove deprecated commands, session-id-less design

- Device labels: lowercase, no whitespace, only a-z 0-9 - _ (enforced at config time)
- Session IDs removed: device label is the sole identifier
- Routes changed: /sessions/:id → /devices/:label
- Removed commands: click, type, find-window, wait-for-window, label, old version, server-version
- Renamed: status → version (compares relay/remote.py/client commits)
- Unified screenshot: takes 'screen' or a window label as argument
- Windows listed with human-readable labels (same format as device labels)
- Single instance enforcement via PID lock file
- Removed input.rs (click/type functionality)
- All docs and code in English
- Protocol: Hello.label is now required (String, not Option<String>)
- Client auto-migrates invalid labels on startup

crates/client/README.md

@@ -1,36 +1,40 @@
-# helios-client (Phase 2 — not yet implemented)
+# helios-client
 
-This crate will contain the Windows remote-control client for `helios-remote`.
+Windows client for helios-remote. Connects to the relay server via WebSocket and executes commands.
 
-## Planned Features
+## Features
 
-- Connects to the relay server via WebSocket (`wss://`)
-- Sends a `Hello` message on connect with an optional display label
-- Handles incoming `ServerMessage` commands:
-  - `ScreenshotRequest` → captures the primary display (Windows GDI or `windows-capture`) and responds with base64 PNG
-  - `ExecRequest` → runs a shell command in a persistent `cmd.exe` / PowerShell session and returns stdout/stderr/exit-code
-  - `ClickRequest` → simulates a mouse click via `SendInput` Win32 API
-  - `TypeRequest` → types text via `SendInput` (virtual key events)
-- Persistent shell session so `cd C:\Users` persists across `exec` calls
-- Auto-reconnect with exponential backoff
-- Configurable via environment variables or a `client.toml` config file
+- Full-screen and per-window screenshots
+- Shell command execution (persistent PowerShell session)
+- Window management (list, focus, maximize, minimize)
+- File upload/download
+- Clipboard get/set
+- Program launch (fire-and-forget)
+- User prompts (MessageBox)
+- Single instance enforcement (PID lock file)
 
-## Planned Tech Stack
+## Configuration
 
-| Crate | Purpose |
-|---|---|
-| `tokio` | Async runtime |
-| `tokio-tungstenite` | WebSocket client |
-| `serde_json` | Protocol serialization |
-| `windows` / `winapi` | Screen capture, mouse/keyboard input |
-| `base64` | PNG encoding for screenshots |
+On first run, the client prompts for:
+- **Relay URL** (default: `wss://remote.agent-helios.me/ws`)
+- **API Key**
+- **Device label** — must be lowercase, no whitespace, only `a-z 0-9 - _`
 
-## Build Target
+Config is saved to `%APPDATA%/helios-remote/config.toml`.
 
+## Device Labels
+
+The device label is the sole identifier for this machine. It must follow these rules:
+- Lowercase only
+- No whitespace
+- Only characters: `a-z`, `0-9`, `-`, `_`
+
+Examples: `moritz_pc`, `work-desktop`, `gaming-rig`
+
+If an existing config has an invalid label, it will be automatically migrated on next startup.
+
+## Build
+
+```bash
+cargo build -p helios-client --release
 ```
-cargo build --target x86_64-pc-windows-gnu
-```
-
-## App Icon
-
-The file `assets/logo.ico` in the repository root is the application icon intended for the Windows `.exe`. It can be embedded at compile time using a build script (e.g. via the `winres` crate).