fix(schemas): add skills field to positionSchema (#83)

The PUT /api/profile/position/:rkey endpoint validated against
positionSchema which did not include a skills field. This caused
400 errors when the frontend sent skill-position linking updates.

Adds an optional skills array (strongRef objects, max 50) matching
the position lexicon definition.

Closes singi-labs/sifa-api#65 (partial)
Ref singi-labs/sifa-web#98

src/routes/schemas.ts

···
   })
   .passthrough();
 
+const strongRefSchema = z.object({
+  uri: z.string(),
+  cid: z.string(),
+});
+
 export const positionSchema = z.object({
   companyName: z.string().min(1).max(200),
   title: z.string().min(1).max(200),
···
   startDate: z.string().optional(),
   endDate: z.string().optional(),
   current: z.boolean().default(false),
+  skills: z.array(strongRefSchema).max(50).optional(),
 });
 
 export const educationSchema = z.object({