WhatsApp parser — raw .txt export → ParsedConversation with unit tests

[Punkte]

What to build

A pure function that takes a raw WhatsApp .txt export and returns a typed ParsedConversation object. Must handle locale variants, multi-line messages, system messages, and omitted media. Covered by unit tests using real export samples.

Acceptance criteria

• parseWhatsApp(rawText: string): ParsedConversation implemented
• Handles EN and FR date/time locale formats
• Multi-line messages (continuation lines) correctly merged
• System messages filtered out ("Messages are end-to-end encrypted", "X added Y")
• <Media omitted> marked as isMedia: true but retained
• Returns participants, dateRange, and normalized messages[]
• Unit tests pass on at least two real export samples

Blocked by

• Project scaffold — monorepo, Fastify, Next.js, Postgres + pgvector, DB schema #1