Teach order types and execution timing with one controlled strategy #110

Affected library: backtest
Current version: 0.1.8
Location: tutorials, docs/user-guide/orders.md, docs/user-guide/execution-semantics.md

Problem

The existing pages describe order and timing settings separately, without a controlled example showing how each changes fills.

Required outcome

Use one strategy and fixed inputs to teach next-bar versus permitted same-bar execution, open versus close fill prices, and market, limit, and stop orders. Show the fill records and explain causal limits.

Acceptance criteria

• Executed configurations produce the displayed, distinct fill times and prices, including an order that remains unfilled.
• No example uses future market information for an earlier decision.
• The tutorial links to relevant book material and the existing task guides.
• Installed-wheel example checks and the strict MkDocs build pass.

Depends on the tutorial inputs and the first-backtest tutorial.