fix(release): bump hard-coded version strings to 0.0.2 + route through MCPP_VERSION

The v0.0.2 release.yml run produced a fully-functional musl-static
binary, but the smoke-test step rejected it because `mcpp --version`
still printed `mcpp 0.0.1`. The version literal had been hand-coded in
four places that the [package].version bump in mcpp.toml didn't reach:

  - src/toolchain/fingerprint.cppm:21  MCPP_VERSION = "0.0.1"
  - src/cli.cppm:64                    "mcpp v0.0.1 — ..." (print_usage)
  - src/cli.cppm:2805                  "mcpp 0.0.1"        (cmd_self_version)
  - src/cli.cppm:2874                  "mcpp 0.0.1"        (--version handler)
  - src/cli.cppm:2947                  .version("0.0.1")   (cmdline App ctor)

Bump the canonical constant in `fingerprint.cppm` to 0.0.2 and refactor
all five sites to read `mcpp::toolchain::MCPP_VERSION` so future bumps
only need a one-line change. The fingerprint constant already drives
the toolchain hash key, so its value matters for cache invalidation
anyway — this consolidates "what version am I" into a single
authoritative location.

Verified locally:
  $ mcpp --version
  mcpp 0.0.2
  $ mcpp self version
  mcpp 0.0.2

Author: Sunrisepeak

src/cli.cppm

@@ -61,7 +61,7 @@ namespace mcpp::cli::detail {
 // canonical printer here so the docs/CHANGELOG examples don't drift
 // every time cmdline tweaks its formatting.
 void print_usage() {
-    std::println("mcpp v0.0.1 — modern C++23 build tool");
+    std::println("mcpp v{} — modern C++23 build tool", mcpp::toolchain::MCPP_VERSION);
     std::println("");
     std::println("Usage:");
     std::println("Project commands:");
@@ -2802,7 +2802,7 @@ int cmd_explain(std::string_view code) {
 // can share `cmd_doctor` / `cmd_env` between top-level and `mcpp self`.
 
 int cmd_self_version(const mcpplibs::cmdline::ParsedArgs& /*parsed*/) {
-    std::println("mcpp 0.0.1");
+    std::println("mcpp {}", mcpp::toolchain::MCPP_VERSION);
     return 0;
 }
 
@@ -2871,7 +2871,7 @@ int run(int argc, char** argv) {
         std::string_view a = argv[1];
         if (a == "--help" || a == "-h") { print_usage(); return 0; }
         if (a == "--version" || a == "-V") {
-            std::println("mcpp 0.0.1");
+            std::println("mcpp {}", mcpp::toolchain::MCPP_VERSION);
             return 0;
         }
     }
@@ -2944,7 +2944,7 @@ int run(int argc, char** argv) {
 
     // ─── Build the top-level App ────────────────────────────────────────
     auto app = cl::App("mcpp")
-        .version("0.0.1")
+        .version(std::string{mcpp::toolchain::MCPP_VERSION})
         .description("modern C++ build tool")
         .option(cl::Option("quiet").short_name('q')
             .help("Suppress status output").global())

src/toolchain/fingerprint.cppm

@@ -18,7 +18,7 @@ import mcpp.toolchain.detect;
 
 export namespace mcpp::toolchain {
 
-inline constexpr std::string_view MCPP_VERSION = "0.0.1";
+inline constexpr std::string_view MCPP_VERSION = "0.0.2";
 
 struct FingerprintInputs {
     Toolchain                       toolchain;