feat: proposals en registry

Añade sistema de proposals al registry: modelos (ProposalKind, ProposalStatus),
CRUD completo (Insert/Get/Update/Delete/List/Search con FTS), validación,
migración 002_proposals.sql y subcomando CLI fn proposal (add/list/show/update).
Motor de migraciones con embed.FS reemplaza schema estático.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

registry/validate.go

@@ -126,6 +126,41 @@ func ValidateFunction(f *Function, knownFunctions, knownTypes map[string]bool) *
 	return nil
 }
 
+// ValidateProposal checks integrity rules for proposals.
+func ValidateProposal(p *Proposal) *ValidationError {
+	var errs []string
+
+	if p.ID == "" {
+		errs = append(errs, "id is required")
+	}
+	if p.Title == "" {
+		errs = append(errs, "title is required")
+	}
+
+	switch p.Kind {
+	case ProposalNewFunction, ProposalNewType, ProposalImproveFunction, ProposalImproveType, ProposalNewPipeline:
+	case "":
+		errs = append(errs, "kind is required")
+	default:
+		errs = append(errs, fmt.Sprintf("invalid kind: %s", p.Kind))
+	}
+
+	switch p.Status {
+	case ProposalPending, ProposalApproved, ProposalRejected, ProposalImplemented, "":
+	default:
+		errs = append(errs, fmt.Sprintf("invalid status: %s", p.Status))
+	}
+
+	if (p.Kind == ProposalImproveFunction || p.Kind == ProposalImproveType) && p.TargetID == "" {
+		errs = append(errs, "target_id is required for improve_* proposals")
+	}
+
+	if len(errs) > 0 {
+		return &ValidationError{ID: p.ID, Errors: errs}
+	}
+	return nil
+}
+
 // ValidateType checks integrity rules for types.
 func ValidateType(t *Type, knownTypes map[string]bool) *ValidationError {
 	var errs []string