pins.yml is dispatch-only, so the drift it exists to report went unreported

[vyncint]

Today — the weekly schedule in pins.yml is commented out (pins.yml:11–13); the workflow is dispatch-only. Its last two runs were 2026-08-24 and 2026-08-31. Upstream has since moved 133 commits and one toolchain, and no issue says so — which is the failure #46 was about, in a new form.

Fix. Re-enable the schedule; add the toolchain channel to the pin set (compare upstream's rust-toolchain.toml to ours) so #1201-style moves are reported; keep the title-dedupe.

Done when

• The workflow has run on schedule at least once and is green on a clean week.
• A toolchain-only upstream change opens the drift issue.