Explicit return values in methods

Be intentional about method return values:
- Methods that perform actions should return meaningful results or self
- Query methods should return the queried value
- Predicate methods (ending in ?) should return true/false
- Bang methods (ending in !) should modify in place or raise

```ruby
# Good: Clear intent
def process_order
validate!
charge_payment
send_confirmation
self # Allow chaining
end

# Good: Predicate returns boolean
def valid? = errors.empty?
```