fix: revert mcpp.toml to legacy dotted-key syntax for bootstrap compat

The release workflow uses a pre-0.0.6 mcpp to bootstrap build. That
old mcpp doesn't understand [dependencies.mcpplibs] as a namespace
subtable. Keep the legacy form so both old and new mcpp can parse it.
Other projects (non-self-hosting) should use the new namespace syntax.

Author: Sunrisepeak

mcpp.toml

@@ -19,11 +19,14 @@ toolchain = "gcc@15.1.0-musl"
 linkage   = "static"
 
 # Eat our own dog food: mcpp uses mcpplibs.cmdline for argument parsing.
-[dependencies.mcpplibs]
-cmdline = "0.0.1"
+# NOTE: uses legacy dotted-key syntax so older bootstrapping mcpp versions
+# (pre-0.0.6, which don't understand [dependencies.<ns>] subtables) can
+# still parse this file during the self-host release build.
+[dependencies]
+"mcpplibs.cmdline" = "0.0.1"
 
 # `mcpp build` ignores [dev-dependencies]; only `mcpp test` resolves them.
-[dev-dependencies.compat]
+[dev-dependencies]
 gtest = "1.15.2"
 
 # Everything else uses M5.0 conventions: