fix(phase-10): add --sources filter flag and DB persistence to recon full

Closes 2 verification gaps:
1. --sources=github,gitlab flag filters registered sources before sweep
2. Findings persisted to SQLite via storage.SaveFinding after dedup

Also adds Engine.Get() method for source lookup by name.

pkg/recon/engine.go

@@ -33,6 +33,14 @@ func (e *Engine) Register(s ReconSource) {
 	e.sources[s.Name()] = s
 }
 
+// Get returns a registered source by name and true, or nil and false.
+func (e *Engine) Get(name string) (ReconSource, bool) {
+	e.mu.RLock()
+	defer e.mu.RUnlock()
+	s, ok := e.sources[name]
+	return s, ok
+}
+
 // List returns registered source names in sorted order.
 func (e *Engine) List() []string {
 	e.mu.RLock()