Add @trails-cool/api package with Zod schemas for REST API contract

Single source of truth for the Journal REST API:
- API_VERSION semver constant (1.0.0)
- Endpoint path constants (routes, activities, auth, uploads, push)
- Zod schemas for all request/response shapes:
  - Routes: list, detail, create, update, compute
  - Activities: list, detail, create
  - Auth: token exchange, refresh, device management
  - Discovery: instance info + API version
  - Uploads: presigned URL flow
  - Errors: structured error response with field-level details
- Cursor-based pagination schemas
- TypeScript types inferred from Zod (z.infer)

Used by Journal server (validation) and mobile client (type safety).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

packages/api/src/uploads.ts

@@ -0,0 +1,17 @@
+import { z } from "zod";
+
+export const PresignedUploadRequestSchema = z.object({
+  filename: z.string(),
+  contentType: z.string(),
+  resourceType: z.enum(["route", "activity"]),
+  resourceId: z.string().uuid(),
+});
+
+export const PresignedUploadResponseSchema = z.object({
+  uploadUrl: z.string().url(),
+  storageKey: z.string(),
+  expiresAt: z.string().datetime(),
+});
+
+export type PresignedUploadRequest = z.infer<typeof PresignedUploadRequestSchema>;
+export type PresignedUploadResponse = z.infer<typeof PresignedUploadResponseSchema>;