feat(proxies): CM-9 backend — polymorphic point-of-contact + resolver

- proxies table (migration 0095, port_id cascade), one per client/interest/yacht
- service: get/set(upsert)/clear + resolveEffectiveProxy (yacht → interest →
  client precedence), port-scoped with entity-in-port guard
- per-entity sub-resource routes (/clients|interests|yachts/[id]/proxy) reusing
  each entity's existing view/edit permission (no new permission resource)
- 3 integration tests (CRUD/upsert, tenant guard, resolution precedence)

Backend only — ProxyCard UI on the 3 detail pages to follow. tsc clean.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/lib/validators/proxies.ts

@@ -0,0 +1,17 @@
+import { z } from 'zod';
+
+/** CM-9: proxy / point-of-contact. */
+
+export const PROXY_ENTITY_TYPES = ['client', 'interest', 'yacht'] as const;
+export type ProxyEntityType = (typeof PROXY_ENTITY_TYPES)[number];
+
+export const setProxySchema = z.object({
+  name: z.string().trim().min(1, 'Name is required').max(200),
+  // Loose contact fields — empty strings are normalised to null in the service.
+  email: z.string().trim().max(320).nullish(),
+  phone: z.string().trim().max(50).nullish(),
+  relationship: z.string().trim().max(100).nullish(),
+  notes: z.string().trim().max(2000).nullish(),
+});
+
+export type SetProxyInput = z.infer<typeof setProxySchema>;