Web generated course data is stale relative to root chapters

[fengjikui]

The canonical root-level course files and the generated web app data are currently out of sync.

Reproduction:

cd web
npm ci
npm run extract
git diff -- web/src/data/generated web/public/course-assets/s09_memory

Observed examples:

• web/src/data/generated/versions.json still reports older s08/s09 line counts and function signatures.
• The web-generated s08/s09/s20 source snapshots omit the newer tool-use/tool-result compaction helpers from the root code.py files.
• web/src/data/generated/docs.json still contains stale chapter text such as the older s03 destructive-command prompt.
• The copied s09 memory subsystem SVG assets differ from the canonical root chapter assets.

Impact: the website can teach/display stale code and metadata even though the runnable root chapters have already moved on.

A focused fix should regenerate the web data/assets from the root chapters and document that workflow in web/README.md so future chapter edits do not leave the site stale again.