fix(release): mirror built userscripts at repo root for GreasyFork sync

[nsheaps-oura]

Summary

Investigated GreasyFork's actual sync-via-webhook implementation (source: lib/github.rb, app/controllers/concerns/webhooks.rb) to figure out why a sync_identifier pointed at this repo wouldn't actually sync. Findings:

• For a GitHub release webhook event, GreasyFork only recognizes a sync URL of the form https://github.com/<owner>/<repo>/releases/latest/download/<file> — which is exactly what each package's @downloadURL/@updateURL already uses.
• To fetch content, it does not download the release asset over HTTP. It resolves that URL back to a git path by stripping the releases/.../download/ prefix and treating whatever's left as the entire repo-relative path (see Github.file_from_root_for_url), then runs git show <release-tag>:<that-path>.
• That means the path it looks for is the flat filename (<pkg>.user.js), not packages/<pkg>/dist/script.user.js. Our dist-commit only ever contained the nested path, so the webhook's git show would have 404'd on every sync attempt.
• Push-event-based sync (the other GreasyFork mechanism) can't work for this repo at all, since it requires the file to be reachable from a branch ref, and this pipeline deliberately keeps built dist/ files out of main's history (tag-only).

Changes

• .github/workflows/release.yaml: the "Commit built userscripts for GreasyFork sync" step now also mirrors each package's built file at the repo root under the flat name matching its release asset (<pkg>.user.js), in addition to the existing nested packages/<pkg>/dist/script.user.js copy. Same dist-commit, same tags (release tag + floating latest).
• Removed scripts/setup-greasyfork-webhook.js — dead code that POSTed a repository_url/webhook_secret JSON body to /en/users/webhook-info, an endpoint/contract that doesn't exist. GreasyFork's webhook setup is a manual one-time step in its own UI; there is no such automation API.

Test plan

• Confirmed via GreasyFork's Rails source that the release-event sync path does git show <release-tag>:<file> with <file> derived as a flat, root-relative name for the releases/latest/download/ URL form.
• Verified the flat filename used here (<pkg-dir-name>.user.js) matches exactly what the existing "Upload userscripts as release assets" step already uploads and what each package's @downloadURL/@updateURL already points at.
• After merge, confirm a real release run adds root-level github-actions-grafana-jump.user.js, github-to-graphite-button.user.js, and graphite-to-github-button.user.js at the new release tag (git show <tag>:<pkg>.user.js).
• Once each script's GreasyFork admin page has its sync URL set (manual step, tracked outside this PR), confirm a real GitHub release triggers GreasyFork's webhook and the listing's code actually updates.

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Generated by Claude Code

[github-actions]

Userscript Version Preview

Preview only — versions and CHANGELOGs are bumped automatically on merge to main, not in this PR. Manual bumps to a higher version are preserved.

Package	Base	New	Action
github-actions-grafana-jump	0.2.2	0.2.3	already-bumped
github-to-graphite-button	0.3.5	0.3.6	already-bumped
graphite-to-github-button	0.3.8	0.3.9	already-bumped