add: cosmofy completions command for shell completions (closes #117)

Generate bash, zsh, and fish completion scripts by parsing usage strings.
Follows baton's philosophy: derive completions from conventions in usage
text rather than requiring additional metadata.

Usage:
  cosmofy completions bash > ~/.bash_completion.d/cosmofy
  cosmofy completions zsh > ~/.zfunc/_cosmofy
  cosmofy completions fish > ~/.config/fish/completions/cosmofy.fish

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

Author: metaist

.cspell.json

@@ -10,11 +10,16 @@
     "CLICOLOR",
     "codeql",
     "cogapp",
+    "compdef",
+    "compgen",
+    "COMPREPLY",
     "compresslevel",
     "cosmofy",
     "docstrings",
     "doctest",
+    "esac",
     "exitmsg",
+    "filedir",
     "fpclose",
     "htmlcov",
     "levelname",
@@ -25,9 +30,9 @@
     "mycommand",
     "mydir",
     "mypackage",
-    "nmycmd",
     "mypy",
     "myscript",
+    "nmycmd",
     "nojekyll",
     "oneline",
     "outl",
@@ -49,9 +54,13 @@
     "pythonversion",
     "removeprefix",
     "setuptools",
+    "subcmd",
+    "subcmds",
+    "subsub",
     "unknowntag",
     "urlopen",
     "venv",
+    "zfunc",
     "zinfo"
   ]
 }

src/cosmofy/__main__.py

@@ -15,6 +15,7 @@
 from .baton import ColorHandler
 from .baton import Command
 from .bundle import cmd as bundle
+from .completions import cmd as completions
 from .fs.__main__ import cmd as fs
 from .self.__main__ import cmd as self
 from .self.version import print_version
@@ -33,6 +34,7 @@
   updater                   install/uninstall bundle self-updater
   fs                        inspect and modify an existing bundle
   self                      manage the `cosmofy` executable
+  completions               generate shell completions
 
 Options:
       --version             display the program version and exit
@@ -75,6 +77,7 @@ def run(args: Args) -> int:
     usage,
     {
         "bundle": bundle,
+        "completions": completions,
         "updater": updater,
         "fs": fs,
         "self": self,