Fix #12: Add more examples to playground

[leftibot]

Automated fix by @leftibot.

What changed

Fix #12: Add examples sidebar and live execution to playground
Adds a sidebar with 12 clickable examples covering all major ChaiScript
features: variables, functions, conditionals, loops, strings, vectors/maps,
lambdas, classes, guards, error handling, and scoping. Clicking an example
populates the editor and auto-runs. Live execution re-evaluates code on
every edit with a 500ms debounce, similar to Compiler Explorer.
Co-Authored-By: Claude Opus 4.6 (1M context) noreply@anthropic.com

Files

 playground.html    | 213 ++++++++++++++++++++++++++++++++++++++++++++---------
 test_playground.sh |  18 +++++
 2 files changed, 195 insertions(+), 36 deletions(-)

Closes #12

Triggered by @lefticus.