feat(env): wire supporter-binary resolution at boot (T-495)

main resolves the override map (and first-run auto-detects, using the
primed login-shell PATH) right after bootSettings.load(), exposing the
process-wide activeSupporterBinaries that tool consumers read — the d2
template (T-494) will resolve its binary through it. Analyze clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

lib/src/env/supporter_binaries.dart

@@ -92,6 +92,11 @@ class SupporterBinaries {
 
 bool _fileExists(String p) => File(p).existsSync();
 
+/// The process-wide resolver, wired at boot via [loadSupporterBinaries]. Tool
+/// consumers (e.g. the d2 template, T-494) read it to resolve a binary; null in
+/// headless contexts where boot wiring hasn't run.
+SupporterBinaries? activeSupporterBinaries;
+
 /// The user-scope SettingsStore key (app layer, `~/.clide`, per-machine) holding
 /// the tool→absolute-path override map.
 const supporterToolsKey = 'app.tools';