Feature: Letters page

[FadyGergesRezk]

Implement the Letters page under /letters.

Priority: P2

API endpoints used

Method	Endpoint	Description
POST	/letters/mail	Send an HTML email to all members
POST	/letters/pdf	Generate a PDF from an HTML template (returns binary)

Tasks

• Add src/features/letters/api/mutations.ts with useSendMail and useGetPdf hooks using TanStack Query mutations
• Add Zod schema to validate the HTML template body is non-empty before submission
• Build a simple HTML template editor (shadcn/ui Textarea) for composing letter content
• Add a "Send Mail" Button that calls useSendMail, disables during submission, and shows a success/error Toast on completion
• Add a "Preview PDF" Button that calls useGetPdf, receives the binary application/pdf response, creates a blob URL, and opens it in a new browser tab
• Both actions should show an error Toast if the request fails

Acceptance criteria

• Composing and sending a mail completes with a visible success Toast
• Clicking "Preview PDF" opens the generated PDF in a new browser tab
• Both buttons are disabled and show a loading state while the request is in flight
• An error Toast is shown if either request fails
• Invalid/non-PDF preview responses are handled with a user-facing error state