feat(schema): add structured learnings DBML model

schema/meta.dbml

@@ -30,3 +30,46 @@ Table tool_annotations {
 
 // Cross-file refs (for relspecgo merge)
 Ref: chat_histories.project_id > projects.guid [delete: set null]
+
+Table learnings {
+  id uuid [pk, default: `gen_random_uuid()`]
+  summary text [not null]
+  details text [not null, default: '']
+  category text [not null, default: 'insight']
+  area text [not null, default: 'other']
+  status text [not null, default: 'pending']
+  priority text [not null, default: 'medium']
+  confidence text [not null, default: 'hypothesis']
+  action_required boolean [not null, default: false]
+  source_type text
+  source_ref text
+  project_id uuid [ref: > projects.guid]
+  related_thought_id uuid [ref: > thoughts.guid]
+  related_skill_id uuid [ref: > agent_skills.id]
+  reviewed_by text
+  reviewed_at timestamptz
+  duplicate_of_learning_id uuid [ref: > learnings.id]
+  supersedes_learning_id uuid [ref: > learnings.id]
+  tags "text[]" [not null, default: `'{}'`]
+  created_at timestamptz [not null, default: `now()`]
+  updated_at timestamptz [not null, default: `now()`]
+
+  indexes {
+    project_id
+    category
+    area
+    status
+    priority
+    reviewed_at
+    tags [type: gin]
+    summary [type: gin]
+    details [type: gin]
+  }
+}
+
+// Cross-file refs (for relspecgo merge)
+Ref: learnings.project_id > projects.guid [delete: set null]
+Ref: learnings.related_thought_id > thoughts.guid [delete: set null]
+Ref: learnings.related_skill_id > agent_skills.id [delete: set null]
+Ref: learnings.duplicate_of_learning_id > learnings.id [delete: set null]
+Ref: learnings.supersedes_learning_id > learnings.id [delete: set null]