feat(10-01): add provider-driven query generator and RegisterAll skeleton

- BuildQueries(reg, source) dedups keywords and formats per-source syntax
- github/gist use 'keyword' in:file; others use bare keyword
- SourcesConfig placeholder struct for Wave 2 plans to depend on
- RegisterAll no-op stub (Plan 10-09 will fill)

pkg/recon/sources/testhelpers_test.go

@@ -0,0 +1,9 @@
+package sources
+
+import "github.com/salvacybersec/keyhunter/pkg/recon"
+
+// newTestEngine returns an empty recon.Engine for tests that need a non-nil
+// engine to exercise registration paths without touching real sources.
+func newTestEngine() *recon.Engine {
+	return recon.NewEngine()
+}