fix(store): protect Version() with mutex to prevent race condition

[yasinlex]

Problem

Version() accessed s.version without synchronization:

func (s *Store) Version() uint64 { return s.version }  // No lock!

While Commit() updates s.version while holding the mutex:

s.mu.Lock()
defer s.mu.Unlock()
// ...
s.version = nextVersion  // Updated under lock

This creates a race condition when Version() is called from:

• RPC handlers (query.go, line 359, 899, 948, 970)
• FSM state (state.go, line 117)
• CLI admin commands (admin.go, line 445)

While Commit() is updating the version.

Fix

func (s *Store) Version() uint64 {
    s.mu.Lock()
    defer s.mu.Unlock()
    return s.version
}

Impact

• Before: Potential data race reading s.version during Commit()
• After: Thread-safe access to s.version via mutex