fix(baileys): resolve @lid senders to a phone number (#362)

[rmyndharis]

Closes #362.

Problem

On the Baileys engine, senderPhone and GET /sessions/:id/contacts/:contactId/phone always returned null for privacy-id (@lid) contacts — the #263 lid→phone feature was effectively non-functional there. Root cause (verified against baileys@6.7.23):

• BaileysSessionStore.resolvePhone() only consulted in-memory mappings populated from contacts.upsert / messaging-history.set lidPnMappings — neither fires for a fresh inbound @lid sender.
• The server-query path used by whatsapp-web.js (getContactLidAndPhone) has no equivalent in baileys@6.7.23 — there is no signalRepository.lidMapping.getPNForLID (confirmed absent in the installed lib), so a runtime lookup wasn't an option.

Fix

Baileys attaches the sender's phone JID right on the inbound message key — senderPn / participantPn alongside senderLid / participantLid (present in the 6.7.23 WAMessageKey type). The adapter now harvests that pair into the session store's lid → pn map at the start of processInboundMessage, before any id canonicalization. As a result:

• the @lid sender of the incoming message resolves to <phone>@c.us, and
• a later GET /contacts/:id/phone for that contact returns the number.

Still best-effort by design (matching the issue): a number is only revealed once WhatsApp delivers the mapping — i.e. after an inbound message from that contact. Truly hidden-number contacts remain null.

Tests (TDD, watched fail first)

• baileys-session-store.spec.ts: 4 cases for recordKeyLidMappings (sender pair, participant pair, canonicalization after learning, ignores empty/half pairs).
• baileys.adapter.spec.ts: 1 end-to-end inbound case — an @lid message whose key carries senderPn resolves from to <phone>@c.us with no prior history-sync mapping.

npx jest → 933/933 pass (86 suites); npm run build + eslint clean.

Notes

• Complements the identity work in feat(engine): engine-neutral WhatsApp identities (Baileys inbound conformance) #342 and the typed-WaId roadmap in [Feature]: typed WaId identity value object + a lid <-> phone resolution table #349.
• No new dependency, no interface change.