chore(stlc): seal custom-code tracking files

[ladyofcode]

Automated by the stlc generate workflow: stlc build re-sealed custom code (after a spec change on main, or after absorbing custom code that landed on a staging repo out of band), updating the tracking files under stainless/custom-code/. Merging brings the config repo in sync with the SDK repos. Safe to merge — tracking-files-only commits are skipped by this workflow, so it won't trigger another build.

[ladyofcode]

Closing: this PR contains no real change. stlc build writes a fresh empty seal commit into each staging repo on every run, and its SHA lands here as base/integrated — but every one of those commits has files=0 and an identical tree (e47029ff80 for python, d7d81c1d43 for typescript, unchanged since 2026-08-24 / 2026-08-31). The SHAs this PR would introduce point at exactly the same content as the ones already on main.

Because allow_auto_merge is off, gh pr merge --auto failed silently and this PR sat open from 2026-09-04, with the 6-hourly cron force-pushing a new head onto it four times a day and mailing every repo watcher each time.

Safe to close — main's current SHAs (7b1a0b41, 34cce754) are pinned by permanent refs/stainless/custom-code/*/base refs in the staging repos, so they can't be garbage collected and the tracking files stay resolvable.

#7 adds a guard that resolves these SHAs to their trees and skips the seal when nothing actually moved, so this won't recur.