fix: correct exit codes and error messages across CLI commands

[bigcat88]

In launch_comfyui background mode, os._exit(process.pid) was passing the process PID (e.g. 12345) as the exit code instead of the actual return code. The foreground mode had a similar issue on one path where exit(res) passed the entire CompletedProcess object instead of res.returncode.

The install, reinstall, and uninstall commands printed "Invalid command: {mode}" when rejecting all as an argument, but mode is the unrelated --mode option (remote/local/cache) which defaults to None, so users saw "Invalid command: None.".

Also fixes a stray ) in the GitHub rate limit error message and a "migit" typo.

[codecov]

Codecov Report

❌ Patch coverage is 57.14286% with 3 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
comfy_cli/command/launch.py	0.00%	3 Missing ⚠️

@@            Coverage Diff             @@
##             main     #388      +/-   ##
==========================================
+ Coverage   70.94%   71.07%   +0.12%     
==========================================
  Files          33       33              
  Lines        3931     3931              
==========================================
+ Hits         2789     2794       +5     
+ Misses       1142     1137       -5     

Files with missing lines	Coverage Δ
comfy_cli/command/custom_nodes/command.py	79.69% <100.00%> (ø)
comfy_cli/command/install.py	76.15% <100.00%> (+0.96%)	⬆️
comfy_cli/command/launch.py	42.68% <0.00%> (ø)

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