Feature/backend api fixes

[SugeethJSA]

enhance contact handling with phone number validation and logging

[celestix]

Required changes — release blocker

Reviewed head: 1f9ae5c4f793f25cbc5aea2ced928d10425316fb.

• api/api.go:145,565-566: 🔴 Full sync enables per-contact app-state events, producing N Wails events, timers, and full frontend refreshes. Suppress incremental events for FromFullSync and emit one coalesced completion event.
• api/contact.go:61-68: 🔴 Drops all LID/hosted contacts, causing valid contacts and names to disappear. Resolve LID→PN, validate/deduplicate aliases, and merge the richest record rather than filtering by server.
• api/chat.go:121-138: 🔴 Chat lookup does not canonicalize LID identities and can format an opaque LID as a phone number. Use one canonical identity helper for lookup/display, format only default-server phone JIDs, and retain the original chat JID for navigation.
• contact refresh path: 🟡 Performs a full GetAllContacts scan for logging and triggers full refreshes for each push/business-name update. Remove diagnostic full scans and coalesce refreshes.
• fetch logging: 🟡 Logs success after a failed fetch. Return/record the error and emit success only after persistence completes.
• tests: 🔴 No tests were added for LID→PN resolution, alias merging, full-sync event counts, duplicate identities, unknown contacts, or chat display/navigation. Add table-driven identity tests plus an integration test asserting exactly one frontend refresh for a full snapshot.

This PR has no dependency-policy violation, but the contact-loss and fan-out behavior must be corrected before merge.