feat: Add mol-ready-work protomolecule (cherry-pick from polecat/immortan)

Adds autonomous backlog processing patrol molecule for crew workers.
The molecule scans PRs, GitHub issues, and beads; selects work using
an ROI heuristic; executes items; and loops until context is low.

Key features:
- Vapor phase (wisp) - ephemeral patrol cycles
- Scans 4 backlogs: PRs > untriaged > beads > triaged
- ROI-based selection with context awareness
- Per-type execution handlers (PR review, triage, implementation)
- Clean handoff protocol with digest squashing

Original commit: 20e2a13 by immortan
Issue: gt-tnca.1

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

internal/beads/builtin_molecules_test.go

@@ -5,8 +5,8 @@ import "testing"
 func TestBuiltinMolecules(t *testing.T) {
 	molecules := BuiltinMolecules()
 
-	if len(molecules) != 12 {
-		t.Errorf("expected 12 built-in molecules, got %d", len(molecules))
+	if len(molecules) != 13 {
+		t.Errorf("expected 13 built-in molecules, got %d", len(molecules))
 	}
 
 	// Verify each molecule can be parsed and validated