chore(.github): drop self fr-gate caller on main (promote #86)

[LukasWodka]

Summary

Promotes the fr-gate-caller.yml removal from #86 up to main, and converges main/develop after the divergence heal.

After this, .github no longer runs its own FR-gate on promotions to its main (it has no deployable environment to functional-review on — RFC-0008 docs-treatment). The reusable fr-gate.yml that every other repo calls is untouched.

Net content diff = the single fr-gate-caller.yml deletion.

Part of #1273 / RFC-0008.

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Note

Low Risk
CI-only change removing a workflow file; no application, auth, or data paths affected.

Overview
Removes the per-repo workflow fr-gate-caller.yml that invoked the reusable tracebloc/.github FR-gate on pull requests targeting staging, main, or master.

This repo will no longer run its own functional-review gate on promotions to main/staging (aligned with RFC-0008: no deployable environment here). The shared reusable workflow fr-gate.yml is unchanged and remains available for other repositories that still call it.

^{Reviewed by Cursor Bugbot for commit 408c33e. Bugbot is set up for automated code reviews on this repo. Configure here.}

[LukasWodka]

👋 Heads-up — Code review queue is at 39 / 30

Above the WIP limit. The team convention is to review existing PRs before opening new work.

Open PRs currently in Code review (oldest first):

• averaging-service#207 — Promote develop → staging · author: @shujaatTracebloc · no reviewer assigned
• backend#1201 — docs(rfc): Data spaces & federated dataset composition (draft) · author: @LukasWodka · no reviewer assigned
• backend#1217 — docs(rfc): Dataset integrity & score reproducibility (draft) · author: @LukasWodka · no reviewer assigned
• backend#1228 — Promote develop → staging · author: @shujaatTracebloc · reviewer: @saadqbal
• backend#1244 — fix(experiments): surface save-time failures as 5xx + guard new NOT NULL columns · author: @LukasWodka · reviewer: @saqlainsyed007
• backend#1251 — docs(bugbot): add .cursor/BUGBOT.md project context (#930) · author: @LukasWodka · no reviewer assigned
• backend#1254 — docs(pr-template): owner-qualify cross-repo closing keywords · author: @LukasWodka · no reviewer assigned
• backend#1259 — docs(rfc): qualified RFC identifiers + org-wide index · author: @LukasWodka · no reviewer assigned
• backend#1261 — RFC-BACKEND-0008: board & process reset (decision RFC — for markup) · author: @LukasWodka · no reviewer assigned
• cli#397 — Release develop → main · author: @shujaatTracebloc · no reviewer assigned

Pull from review before opening new work. (This is a nudge from the kanban WIP check, not a block.)