Refresh the host imports before each host cuts over

The host trees were imported at pinned commits so each import was reproducible and verifiable
against its source. The tradeoff is that they are snapshots, and development continues in the
app repositories until each host cuts over.

Current drift:

This is not a correctness problem. Nothing builds or consumes the trees yet, so a stale
snapshot breaks nothing. It matters at cutover: whoever moves first needs the tree to be
current, and the refresh gets more awkward the longer it waits.

Worth doing once, immediately before a host cuts over, rather than repeatedly. Refreshing
on a schedule is churn against a tree nothing reads yet.

Same procedure as the original imports, and the same checks earned their keep there: compare
blob hashes against the source rather than eyeballing a diff, and confirm nothing is dropped
by an ignore rule. The Android import lost 57 files that way and the hash comparison is what
caught it.

Depends on: the host's CI landing, so #680 for iOS.

Steps

• Re-extract the tree at a fresh recorded commit
• Confirm blob hashes match the source, except deliberate deviations
• Confirm no file is dropped by an ignore rule
• Record the new source commit in the commit message

Done when

The host tree matches its source at a recorded commit taken shortly before cutover.