[chore] store layer uses context.Background everywhere, no HTTP context propagation

[nkanf-dev]

Problem

All SQLite operations in internal/store/sqlite.go use context.Background():

func (s *SQLiteStore) AppendEvent(event types.EventEnvelope) error {
    _, err := s.db.ExecContext(context.Background(), ...)

This pattern repeats across all 22+ StateStore methods and 4 EventStore methods. HTTP request contexts (with cancellation, deadlines, trace IDs) are not propagated from handlers through the engine to the store layer.

Impact

• No cancellation: if an HTTP client disconnects, the SQLite query still runs to completion
• No deadlines: slow queries can block indefinitely (mitigated by SQLite's busy_timeout pragma, but not by request-level timeouts)
• No tracing: cannot correlate a slow DB operation back to the originating HTTP request

Expected

Pass context.Context from HTTP handlers through Engine methods to store operations. This requires:

1. Adding context.Context as the first parameter to all EventStore and StateStore interface methods
2. Threading context through Engine's public methods (Decide, Report, ResolveApproval, etc.)
3. Updating all callers in httpapi/router.go

Key code

• internal/store/sqlite.go — all methods use context.Background()
• internal/core/engine.go — Engine methods don't accept context
• internal/httpapi/router.go — HTTP handlers have r.Context() but don't pass it

[nkanf-dev]

Fixed by propagating context.Context from the HTTP router through the Engine subsystems to the SQLite store layer, enabling better timeout control and tracing support.