chore: migrate deps to namespace syntax (mcpp 0.0.6)

Updates mcpp.toml to use explicit namespace fields:
- [package].namespace added
- [package].name uses short name only
- [dependencies.compat] / [dev-dependencies.compat] for non-modular libs
- [dependencies.mcpplibs.capi] for C API wrappers

Author: Sunrisepeak

mcpp.toml

@@ -1,16 +1,14 @@
 [package]
-name        = "mcpplibs.cmdline"
+namespace   = "mcpplibs"
+name        = "cmdline"
 version     = "0.0.2"
 description = "A simple command-line parsing library/framework for modern C++"
 license     = "Apache-2.0"
 authors     = ["mcpplibs"]
 repo        = "https://github.com/mcpplibs/cmdline"
 
-# Library target — exposes module `mcpplibs.cmdline` to dependents.
-# Sources default to src/**/*.{cppm,cpp,cc,c}; tests/ and examples/ are
-# discovered separately (`mcpp test` / standalone builds).
 [targets.cmdline]
 kind = "lib"
 
-[dev-dependencies]
+[dev-dependencies.compat]
 gtest = "1.15.2"