feat(app): install the openidea command on macOS, Windows and Linux (#2009)

Adds Install/Uninstall 'openidea' Command actions. macOS uses the bundle launcher, Windows a user PATH wrapper and named pipe, and Linux the executable/AppImage path with a PATH hint. Files, folders, positions and `diff` go to the running app or start it.

Closes #1286

Co-authored-by: jaw52 <[email protected]>

docs/command-line.md

@@ -0,0 +1,41 @@
+# Command-line launcher
+
+Install the `openidea` command from **OpenIDEA → Install 'openidea' Command** on
+macOS, or **Tools → Install 'openidea' Command** on Windows and Linux. The same
+action is available in Find Action. Open a new terminal after installation.
+
+- **macOS:** move OpenIDEA to Applications first. The command links to the launcher
+  inside the app bundle. It uses `~/.local/bin` when that directory is on PATH;
+  otherwise it uses `/usr/local/bin` and may request an administrator password.
+- **Windows:** installation creates `openidea.cmd` in
+  `%LOCALAPPDATA%\OpenIDEA\bin` and adds that directory to the user PATH. This
+  works with installed and portable copies, without administrator rights.
+- **Linux:** installation creates `~/.local/bin/openidea`. If another command
+  takes precedence or this directory is absent from PATH, the notification asks
+  you to put it at the beginning of your shell's PATH. For Bash and Zsh, add
+  `export PATH="$HOME/.local/bin:$PATH"` to your shell profile. For Fish, run
+  `fish_add_path --prepend ~/.local/bin`. An AppImage launcher targets the original
+  AppImage; keep that file in a permanent location.
+
+```sh
+openidea .
+openidea src/main.rs README.md
+openidea --line 12 --column 5 src/main.rs
+openidea src/main.rs:12:5
+openidea diff before.txt after.txt
+openidea --help
+openidea --version
+```
+
+Folders open as projects. Files open in their project's window, or in LightEdit
+when no project contains them. Lines and columns start at 1. With no paths, the
+command focuses OpenIDEA. It starts the app if necessary and returns after handing
+off the request. Unknown options and missing files exit with code 1.
+
+Use `--` before a filename beginning with `-`, or before a file named `diff`.
+The existing GUI executable and OS file associations still work.
+
+**Uninstall 'openidea' Command** removes only OpenIDEA's launcher, and on Windows
+its dedicated user PATH entry. A command belonging to another application is
+never overwritten or removed. Reinstall the command after moving a portable
+copy or AppImage to a different location.