fix: correct Legacy Code examples, a curriculum link, and the index page title

[megabyde]

Third of three stacked PRs, replacing #53. #54 and #55 are merged, so this targets main directly.

Two commits. The first corrects what the Legacy Code decks teach; the second silences a pandoc warning in the index build. Squash-merging collapses them, so the title above covers both.

8cbc205 — what the decks teach

Wrap Class demonstrated inheritance, not wrapping

05-safe-changes.md illustrated the Wrap Class technique with class LoggingEngine(Engine) calling super().calculate_torque(...). That is subclassing. The wrapper now holds an injected Engine and delegates to it, and the comparison table row that described the technique's location of change as Subclass is corrected to Wrapper.

The sprouting kata asked for something sprouting cannot do

06-kata-sprouting-wrapping.md instructed readers to add new authentication logic and "do not modify the original method". Sprouting requires a minimal change at the call site, so the task as written was unsatisfiable. Reworded to ask for exactly that minimal change, and the corresponding testing task now refers to the original entry point rather than a "legacy method" that no longer exists as described.

The invoice characterization test expected the wrong number

03-safety-net.md asserted Approx(1850.95). Walking the calculator shown on the same slide over its three line items gives 500, then 1368, then 2132.1. Corrected to Approx(2132.10).

The tax characterization test was a tautology

The Python example built a results dict by calling calc.calculate_tax(*case), then asserted that calc.calculate_tax(*case) equalled it. That passes for any implementation, including a broken one, which is the opposite of the lesson on the slide. It now records the six expected outputs directly. All six were checked against the TaxCalculator shown above them: NY 30k -> 1200, NY 60k -> 3600, NY 120k -> 10800, CA 50k -> 1500, CA 80k -> 5600, TX 45k -> 450.

null in C++

02-kata-identifying.md compared a pointer against null in the singleton example. Now nullptr.

Curriculum link

The Advanced TDD row 4 C++ Mars Rover link pointed at mars-rover-python-kata. Row 5 already had it right, so the two rows disagreed.

7b3d53d — pandoc title metadata

index.template.html hardcoded the <title> element, so pandoc saw no title metadata and warned on every build:

[WARNING] This document format requires a nonempty <title> element.
  Defaulting to 'README' as the title.

The page was always correct; pandoc just had no way to know. The title now comes from --metadata title="Clean Code Slides" and the template reads $pagetitle$, so there is one source for it. Generated output is byte-identical to before.