Feature/slog

[SugeethJSA]

S log implemented pls check, no logcat.

[celestix]

Required changes — release blocker

Reviewed head: f554c63bcf46fbffab50bc238f660cfca3f45432.

• api/api.go:396-402: 🔴 Requests "sqlite" while the retained mattn driver registers "sqlite3"; application startup fails. Restore "sqlite3" and add an actual startup test.
• api/api.go:190-216,631-635: 🔴 Custom reconnect competes with whatsmeow's built-in reconnect and can repeatedly observe ErrAlreadyConnected while exposing a false disconnected state. Use whatsmeow's reconnect/status hooks as the single authority.
• api/api.go:168-180: 🔴 Purge targets nonexistent nick_name, bypasses the store/cache lifecycle, and mutates dependency-owned schema. Remove the purge; manage application-owned contact state through public store APIs and canonical JIDs.
• api/api.go contact handler: 🟡 Full-sync updates fan out one Wails event/frontend refresh per contact. Skip incremental emissions for FromFullSync and emit one coalesced snapshot-complete event.
• api/contact.go:44-47: 🔴 One unknown participant aborts the entire group response. Return a fallback participant DTO and continue collecting the group.
• HistorySync handler: 🟡 Starts a goroutine for each batch without ordering or bounded backpressure. Route batches through one cancellable serialized processor.
• logging: 🟡 Eager fmt formatting defeats structured logging, duplicates records, and exposes raw JIDs/paths. Pass structured attributes lazily and redact identifiers.
• frontend reconnect notifications: 🟡 Notification IDs/listeners can be overwritten and leaked. Keep one stable subscription and unsubscribe with the exact registered callback.
• tests: 🔴 No tests were added; passing package tests do not execute Startup, reconnect races, full-sync fan-out, or unknown-participant handling. Add these tests before re-review.

The standard-library slog direction is acceptable and does not add a logcat dependency. Extract it into a small logging-only PR after removing the unrelated database/reconnect/contact behavior.