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/models.go

@@ -87,6 +87,42 @@ type Type struct {
 	UpdatedAt  time.Time `json:"updated_at"`
 }
 
+// ProposalKind classifies a proposal.
+type ProposalKind string
+
+const (
+	ProposalNewFunction     ProposalKind = "new_function"
+	ProposalNewType         ProposalKind = "new_type"
+	ProposalImproveFunction ProposalKind = "improve_function"
+	ProposalImproveType     ProposalKind = "improve_type"
+	ProposalNewPipeline     ProposalKind = "new_pipeline"
+)
+
+// ProposalStatus represents the review state of a proposal.
+type ProposalStatus string
+
+const (
+	ProposalPending     ProposalStatus = "pending"
+	ProposalApproved    ProposalStatus = "approved"
+	ProposalRejected    ProposalStatus = "rejected"
+	ProposalImplemented ProposalStatus = "implemented"
+)
+
+// Proposal represents a suggested improvement to the registry.
+type Proposal struct {
+	ID          string         `json:"id"`
+	Kind        ProposalKind   `json:"kind"`
+	TargetID    string         `json:"target_id"`
+	Title       string         `json:"title"`
+	Description string         `json:"description"`
+	Evidence    map[string]any `json:"evidence"`
+	Status      ProposalStatus `json:"status"`
+	CreatedBy   string         `json:"created_by"`
+	ReviewedBy  string         `json:"reviewed_by"`
+	CreatedAt   time.Time      `json:"created_at"`
+	UpdatedAt   time.Time      `json:"updated_at"`
+}
+
 // GenerateID builds the canonical ID: {name}_{lang}_{domain}
 func GenerateID(name, lang, domain string) string {
 	return name + "_" + lang + "_" + domain