IWardrobeRepository / WardrobeFunctions: Missing contract documentation on public interface and HTTP endpoints

## Problem

`PluckIt.Core/IWardrobeRepository.cs` has no XML documentation on any method. `PluckIt.Functions/Functions/WardrobeFunctions.cs` HTTP endpoints have no documentation on accepted query parameters, request body shape, or returned error codes (400/401/404/422/500).

## Impact

New developers must read through implementation code to understand contracts. API clients (including the Angular frontend) have no specification for error handling.

## Proposed Fix

- Add XML ``, ``, ``, and `` tags to all public interface methods in `IWardrobeRepository`.
- Add a comment block to each `[Function]` handler in `WardrobeFunctions.cs` listing HTTP method, route params, request body schema, and possible error responses.

## Functionality Impact

No runtime change; improves developer experience and reduces onboarding friction.