chore(release): 2026.8.19.1 — bare-metal targets and BSP-supplied target worlds

Ships `--target riscv64-none-elf` / `riscv32-none-elf`: mcpp builds a
freestanding image from C++20 modules and `mcpp run --target-triple` boots it
through a per-target `runner` template, with the C library, startup code,
memory layout and ISA profile all supplied by an ordinary dependency package
(#455).

New surface a package can use:
  * `mcpp:link-script=` / `mcpp::link_script(p)`  — reaches the consumer's link
  * `mcpp::xpkg_dir(ns, name)`                     — where an [xlings] deps payload landed
  * `[target.<triple>].runner`                     — how to execute what this host cannot

Author: speak-agent

mcpp.toml

@@ -1,6 +1,6 @@
 [package]
 name        = "mcpp"
-version = "2026.8.18.3"
+version = "2026.8.19.1"
 description = "Modern C++ build & package management tool"
 license     = "Apache-2.0"
 authors     = ["mcpp-community"]

src/version.cppm

@@ -31,6 +31,6 @@ import std;
 
 export namespace mcpp {
 
-inline constexpr std::string_view MCPP_VERSION = "2026.8.18.3";
+inline constexpr std::string_view MCPP_VERSION = "2026.8.19.1";
 
 } // namespace mcpp