feat(validators): adopt drizzle-zod for tags + brochures schemas

Pilot adoption of `drizzle-zod` (already shipped as part of `drizzle-orm`).
Two CRUD-shape validators migrate from hand-written z.object() to
`createInsertSchema(table, refinements)`:

- tags: name + color (with hex regex refinement).
- brochures: label + description + isDefault.

Both schemas now derive directly from the Drizzle table definition.
Adding a column to the table will auto-include it in the validator
(filtered via `.pick(...)` where API surface should stay narrower than
the table). Eliminates the validator-drift class of bugs the audit
flagged (e.g. adding a column to clients but forgetting to add it to
createClientSchema).

Pattern is established for future validator touches. Migrating the
remaining CRUD validators is opportunistic — done when the validator
file is otherwise being edited.

Verified: tsc clean, vitest 1293/1293 pass.

Co-Authored-By: Claude Opus 4.7 (1M context) <noreply@anthropic.com>

src/lib/validators/brochures.ts

@@ -1,16 +1,19 @@
 import { z } from 'zod';
+import { createInsertSchema, createUpdateSchema } from 'drizzle-zod';
 
-export const createBrochureSchema = z.object({
-  label: z.string().trim().min(1).max(120),
-  description: z.string().max(500).optional().nullable(),
-  isDefault: z.boolean().optional(),
-});
+import { brochures } from '@/lib/db/schema/brochures';
 
-export const updateBrochureSchema = z.object({
-  label: z.string().trim().min(1).max(120).optional(),
-  description: z.string().max(500).optional().nullable(),
-  isDefault: z.boolean().optional(),
-});
+// Derived from the Drizzle table — adding a column to `brochures`
+// auto-includes it here. Refinements override per-field.
+export const createBrochureSchema = createInsertSchema(brochures, {
+  label: (s) => s.trim().min(1).max(120),
+  description: (s) => s.max(500),
+}).pick({ label: true, description: true, isDefault: true });
+
+export const updateBrochureSchema = createUpdateSchema(brochures, {
+  label: (s) => s.trim().min(1).max(120),
+  description: (s) => s.max(500),
+}).pick({ label: true, description: true, isDefault: true });
 
 export const registerBrochureVersionSchema = z.object({
   storageKey: z