ci(staging-v2): merge fitted experimental BKT params instead of copying default

[mjyang00001]

Companion to #118 and #126 — the third and last content workflow carrying the same line.

staging-content-update.yml (branch staging-v2, same 0 3,15 * * * cron) ends its "Move and prepare files" step with cp defaultBKTParams.json experimentalBKTParams.json, making the two A/B slots byte-identical and discarding any fitted values. This replaces the copy with bkt/merge_experimental.py from the already-cloned OATutor-Tooling checkout: for each KC in the freshly generated default file it takes the fitted value where one exists, else default's own value — so experimental tracks default's live KC set while keeping tuned values.

This is a full run (rm -rf of the content dir followed by final.py online full), so default is complete by construction and no restore step is needed, unlike the incremental path in #126.

Depends on CAHLR/OATutor-Tooling#16, which adds bkt/merge_experimental.py and bkt/output/experimentalBKTParams.json. The workflow clones tooling's default branch, so that PR must merge first or the step will fail.

Test plan

• Merge Feature/bkt fitting OATutor-Tooling#16 first
• workflow_dispatch this workflow and confirm the merge step reports the fitted-KC count
• Verify experimentalBKTParams.json on staging-v2 differs from defaultBKTParams.json and has the same KC set
• No "BKT Parameter does not exist" errors in the browser console

🤖 Generated with Claude Code

https://claude.ai/code/session_014Uq7T4wTcGUWnMAbKyPHQ3