feat: add form templates

- Add isTemplate and templateName fields to forms
- Add listTemplates and createFromTemplate API endpoints
- Add template selection to new form page UI
- Add sample templates and forms to seed script:
  - Informed Consent template
  - Post-Session Survey template
  - Demographics questionnaire template

src/server/db/schema.ts

@@ -630,6 +630,8 @@ export const forms = createTable(
     description: text("description"),
     version: integer("version").default(1).notNull(),
     active: boolean("active").default(true).notNull(),
+    isTemplate: boolean("is_template").default(false).notNull(),
+    templateName: varchar("template_name", { length: 100 }),
     fields: jsonb("fields").notNull().default([]),
     settings: jsonb("settings").default({}),
     createdBy: text("created_by")